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

Results foralpha.file.questbound.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2023-07-13T21:56:01.192	2023-07-13T00:00:00	2024-08-10T23:59:59	alpha.file.questbound.com	alpha.file.questbound.com	C=US, O=Amazon, CN=Amazon RSA 2048 M01
2023-04-14T22:11:21.62	2023-04-14T00:00:00	2024-05-12T23:59:59	alpha.file.questbound.com	alpha.file.questbound.com	C=US, O=Amazon, CN=Amazon RSA 2048 M01
2023-04-14T18:20:46.729	2023-04-14T00:00:00	2024-05-12T23:59:59	alpha.file.questbound.com	alpha.file.questbound.com	C=US, O=Amazon, CN=Amazon RSA 2048 M01
2023-04-14T18:20:46.533	2023-04-14T00:00:00	2024-05-12T23:59:59	alpha.file.questbound.com	alpha.file.questbound.com	C=US, O=Amazon, CN=Amazon RSA 2048 M02