SDK
Software development kit
An SDK is a set of tools published by a vendor to integrate its service into an application: a code library, documentation and examples, bundled so you do not have to write the integration yourself.
SDK, API, library: the difference
An API is an exchange contract: it describes what you can ask a service for, and in what form. A library is reusable code. An SDK bundles both and adds what it takes to work — configuration, debugging tools, examples. Put another way: the API tells you what to call, the SDK saves you writing the call.
In audience measurement
The SDK is the script you put on your site. It decides what gets collected, and therefore your compliance: its size weighs on how fast your pages load, and what it writes on the visitor’s device — cookie, local storage, persistent identifier — determines whether a consent banner is needed. Two questions to ask before installing one: how much does it weigh, and what does it store?