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

Results forwebdisk.traincycle.org

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2020-07-07T09:17:50.776	2020-07-07T08:17:50	2020-10-05T08:17:50	cpcontacts.traincycle.org	webdisk.traincycle.org	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-07-07T09:17:50.635	2020-07-07T08:17:50	2020-10-05T08:17:50	cpcontacts.traincycle.org	webdisk.traincycle.org	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-06-24T05:07:11.305	2020-06-24T04:07:11	2020-09-22T04:07:11	traincycle.org	webdisk.traincycle.org	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-06-24T05:07:11.17	2020-06-24T04:07:11	2020-09-22T04:07:11	traincycle.org	webdisk.traincycle.org	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-04-23T16:47:58.863	2020-04-23T15:47:58	2020-07-22T15:47:58	traincycle.org	webdisk.traincycle.org	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
2020-04-23T16:47:58.673	2020-04-23T15:47:58	2020-07-22T15:47:58	traincycle.org	webdisk.traincycle.org	C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3