API keys allow external applications to integrate with your site.

API keys consist of two parts separated by a semi-colon (:).   The first part is the key id and the second part if the key secret.  Depending upon the integration you may be use the whole key or just the key id.

Here is an example of an API key:

5f763875f7ab1500083a7b30:629415672d6dea25f6485b5dc482391a0e2cb733c97f087d95f5508f28aa0157

More information: