Based on in the information I have gathered:
On using command gpg -K
which lists secret keys:
sec
: the master/primary secret key. There is key size, keyid, creation date, expiration date and fingerprint information displayed.
ssb
: secret subkeys. These can be your sub signing key, encryption key or authentication key. You can have multiple subkeys.
uid
: this is the user information associated with the secret key. You can have multiple uids.
sec#
: # after sec means that your secret key is missing from the machine. But it has a reference to the secret key.
ssb>
: > after ssb means that your subkeys are not the machine. Instead they are on a smartcard.
On using command gpg -k
which lists public keys:
pub
: your public key info.
sub
: your public subkey info.
If you have any other information which is missing. Please edit the answer or leave a comment.
Thanks to @Nalaurien for the previous answer.