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

Results for*.rainbowcd.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-06-13T15:41:37.182	2020-06-13T14:41:36	2020-09-11T14:41:36	rainbowcd.com	*.rainbowcd.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-06-13T15:41:37.182	2020-06-13T14:41:36	2020-09-11T14:41:36	rainbowcd.com	*.rainbowcd.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-06-13T15:41:37.055	2020-06-13T14:41:36	2020-09-11T14:41:36	rainbowcd.com	*.rainbowcd.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-06-13T15:41:37.055	2020-06-13T14:41:36	2020-09-11T14:41:36	rainbowcd.com	*.rainbowcd.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-03-22T06:16:58.829	2020-03-22T05:16:58	2020-06-20T05:16:58	forbideneast.com	*.rainbowcd.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-03-22T06:16:58.829	2020-03-22T05:16:58	2020-06-20T05:16:58	forbideneast.com	*.rainbowcd.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-03-22T06:16:58.683	2020-03-22T05:16:58	2020-06-20T05:16:58	forbideneast.com	*.rainbowcd.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-03-22T06:16:58.683	2020-03-22T05:16:58	2020-06-20T05:16:58	forbideneast.com	*.rainbowcd.com	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3