It can be anything! An apex, subdomain, or even a URL.

Results forapi3.candidatehq.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2018-11-15T19:55:56.672	2018-11-15T18:55:55	2019-02-13T18:55:55	api3.candidatehq.com	api3.candidatehq.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-11-15T19:55:55.816	2018-11-15T18:55:55	2019-02-13T18:55:55	api3.candidatehq.com	api3.candidatehq.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-08-25T20:48:16.614	2018-08-25T19:48:16	2018-11-23T19:48:16	api3.candidatehq.com	api3.candidatehq.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-08-25T20:48:16.339	2018-08-25T19:48:16	2018-11-23T19:48:16	api3.candidatehq.com	api3.candidatehq.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-06-04T21:45:39.924	2018-06-04T20:45:39	2018-09-02T20:45:39	api3.candidatehq.com	api3.candidatehq.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2018-06-04T21:45:39.716	2018-06-04T20:45:39	2018-09-02T20:45:39	api3.candidatehq.com	api3.candidatehq.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3