> ## Documentation Index > Fetch the complete documentation index at: https://docs.ionq.com/llms.txt > Use this file to discover all available pages before exploring further. # Glossary > An glossary of IonQ Platform terminology This is a glossary of terms relating to the [IonQ Quantum Cloud Platform](https://cloud.ionq.com) and the APIs and SDKs that integrate with it. To learn *quantum computing* terminology, visit the ["Quantum Glossary"](https://ionq.com/resources/glossary) on our Resource Center. ## Platform Concepts #### API An *application programming interface*, or API, allows an external user to interact with a specific system or service. In the case of the [IonQ Quantum Platform's API](/api-reference), it takes the format of a "RESTful" HTTP interface. Users can interact directly with the API via command-line tools like `curl` or Python libraries like `requests`, or they can interact with the IonQ Quantum Platform via an [SDK](#sdk) like Qiskit. *** #### API Key To access an API you need to *authenticate* yourself using an API key. This is a special type of password used to access our systems via API. Keys are attached to [Projects](#project), and are created on [cloud.ionq.com](https://cloud.ionq.com/settings/keys). To learn more, read our guide on [Managing API Keys](/guides/managing-api-keys). *** #### Backend A [backend](/user-manual/backends) is a system that [jobs](#job) can be submitted to. A backend can either be a [QPU](#qpu) (a quantum computer) or a [simulator](#simulator). *** #### Characterizations A characterization is a snapshot of a the performance characteristics of a [hardware backend](backends) at a moment in time, including fidelity (error rate) and gate speed information. *** #### Circuit A representation of a quantum computation, made up of a series of qubit initializations, gates, and measurements. They can be submitted to a QPU as a part of a [job](#job). *** #### Execution Executions are created by a [job](#job) to run a specific circuit on a QPU. The number of times it will be repeated and measured is expressed as [shots](#shot). *** #### Hybrid "Hybrid" is a general term used to refer to when a QPU co-processes with a classical computing system. Commonly, this is used to run an [optimization algorithm](https://en.wikipedia.org/wiki/Mathematical_optimization) for optimizing a variational quantum circuit. A hybrid workflow will contain many [jobs](#job) as the algorithm optimizes the circuit. *** #### Job A task to be completed by our system. This can be one or more [circuits](#circuit) in a variety of formats, or instructions for the IonQ platform for a specific type of workload task. A job may also be a *parent job* (created during a multicircuit job submission), which triggers the creation of additional *child jobs* for individual circuits. *** #### Job Status As jobs progress through the platform, they move through different states. Job status can be viewed on the [My Jobs](https://cloud.ionq.com/jobs) page of the IonQ Cloud Console or on a specific [project's](#project) page for jobs submitted to that project, as well as accessed via the API or an SDK. The possible statuses are listed in the [user manual's Jobs page](/user-manual/jobs). *** #### Job Queue Once submitted, jobs are decomposed into executions which are then added to a queue. The queue is served in a prioritized model based on a [fair-sharing](https://en.wikipedia.org/wiki/Fair-share_scheduling) schedule. *** #### Reservation A reservation is a pre-scheduled block of time where a single user or organization is given access to a specific QPU. To make a reservation, reach out to your IonQ point of contact or email [support@ionq.co](mailto:support@ionq.co) with information about the workload, target system, and scheduling considerations. *** #### SDK A set of libraries or tools that ease the integration or interaction with another computing system. For example, common "quantum SDKs" are [Qiskit](https://qiskit.org/), [Cirq](https://quantumai.google/cirq), or [PennyLane](https://pennylane.ai/). IonQ offers plug-ins and integrations for many SDKs, which enable easier interaction with the IonQ API. *** #### Shot A single measurement of a given [circuit](#circuit) on a QPU. Given the nature of quantum circuits, many shots are required for an accurate representation of the circuit's output. *** #### Simulator A *simulation* of a quantum computer, made available as a backend in our system. Simulators mimic the behavior of quantum computers by following the rules of quantum mechanics--giving users the ability to test circuits without running them directly on a QPU. *** #### Solver A packaged tool that takes in an input, creates a circuit, runs it on a QPU, evaluates the results, and optimizes the circuit until a goal is hit. *** #### QPU A quantum computer, made available as a backend in our system. In IonQ's case, one that [employs individual atoms an ion trap](https://ionq.com/technology) as qubits. *** ## Administrative Concepts #### Organization An group consisting of many users and projects that can be granted QPU access through a contract. [Learn more](/user-manual/organizations). *** #### Project Projects allow multiple users to submit jobs to a single, shared place. Users can be added to a project by an organization owner, and when jobs are submitted, they must be submitted to a specific project. Organization owners can set a [budget](#budget) on each project. [Learn more](/user-manual/projects). *** #### User An individual user's account in an organization which is assigned a specific role that defines what permissions they have. [Learn more](/user-manual/accounts). *** #### User Role A set of permissions assigned to a given user. Currently the roles can be: * **Users:** A normal user. * **Organization owner:** Can manage projects and users in the organization. *** ## Billing Concepts #### Allocation An amount of access time to a QPU (or other system) granted through a contract from which [job usage](#usage) is deducted. Allocations are also evaluated as part of [job queueing](#job-queue) process, and are one determinant of how priority is set. *** #### Budget Budgets are spending limits that can be added by an organization owner to a project that, when hit, will prevent further jobs from being submitted. [Learn more](/user-manual/projects#adding-or-changing-a-project-budget). *** #### Contract A legal agreement setting the rate, [allocation](#allocation), and other terms for access to IonQ's backends and other systems. Note that a contract is required for access to a QPU; contact [sales@ionq.co](mailto:sales@ionq.co) for more information. *** #### Cost Cost represents how much your organization will pay for something. In the case of jobs, this is the amount of [usage](#usage) multiplied by the rate specified in your contract for the backend it was run on. *** #### Usage The time it took to run a given job on a backend. Usage is aggregated contextually--for example, how much a [project](#project) "used" would refer to the aggregate usage of all jobs submitted to that project in the given period.