Glad is how you feel when you hear that something nice happened to someone you care about, or when you learn you got an A on that test you studied so hard for. It means happy or pleased.
Glad doesn't quite mean jumping for joy — it's more a state of contentment and pleasure. You're glad to hear from an old friend who calls you out of the blue and glad to meet your friendly new neighbors. Glad can also mean "eagerly willing" so you might say, "I'll be glad to taste test those brownies for you!" The Old English source is glæd, "gleaming, joyous, or gracious."