ASTRO is convention used over a 1N opening to show 2-suited hands:

2 shows Hearts and a minor

2 shows Spades and another suit

Partner ("advancer") bids the major with 4+ or with 3 to an honor; otherwise, he bids the cheapest suit.

With an invitational hand, advancer jumps in the major if he has a fit; otherwise, he bids 2N.

Over intervention, advancer doubles to show support for the major and invitational strength. With a weak hand, advancer bids the major with support.