Lord

The term Lord is an honorific used to indicate that a man or his father has rank. It is used for a marquis, earl, count, viscount, baron or baronet or the son of duke or marquis. It came to be extended to non-peerage ranks, eg. Lord Mayor or Lord Chamberlain, and church ranks, eg. Archbishop of Canterbury, Lord Clancy.

For landed peers, it is used with the name of their estate, not their first name. Hence, you could refer to the Earl of Cumnor as Lord Cumnor.

a Lord in the SCA

Lord is the honorific given in the SCA to male holders of an Award of Arms or Kingdom level award. Any male participants are entitled to be called m'lord as a polite form of address but this implies no rank.

Other ranks tend to use different honorifics, eg. Your Excellency for barons.