~2/1: What Does 1S-3D Mean?

The bid (1M-3m) is played in a couple of ways:
~One popular way is that the sequence shows a weak hand of about 5-8 HCP with the HCP in the bid minor suit  of 6+ cards–or something like this:
S 3
H A43
D QT98654
C 76
Here the points are not in the long minor suit, but with the solidity of the suit and an almost-sure trick in the heart ace, the trick-taking capability of the hand (5+ tricks) is sound.

~Another popular meaning of 1M-3m is an invitational bid of near-opening value with a long suit. The hand might look something like
S 3
H K43
D KJT986
C Q43

A third method of responding to 1 of a major with a long minor and 10+ HCP is to respond 2C with this hand:
S 3
H A97
D QT
C KQT8765
Partner will take the 2C bid as a game force unless responder rebids 3C. After the repeat of the minor suit, opener will recognize this near-opening hand with a long minor.

It is important that the partnership have a bidding understanding for these hands.