Apricot glaze is an apricot jelly (strained jam), used to coat tarts, to protect them from the air and give them a glossy appearance.
If you intend to buy: You will find it in supermarket, or in specialized stores, where it's cheaper. See about that my best addresses page.
If you want to use it: Apricoting glaze looks like a fruit jelly, and should be melted with 10% water or sugar syrup, in a bain-marie or microwave oven before use.