Yes, lilies bloom only once a year. Sometimes you'll see a seller refer to a lily as a "rebloomer" but that is incorrect. Those lilies (generally oriental-trumpets) have secondary buds that extend the bloom time, but don't have a second set of buds that grow in later and then bloom.

Asiatics bloom in late spring. They are followed by Longiflorum, Trumpets, and then Orientals, in early, mid, and late summer respectively. The interspecific hybrids can have a bloom time inbetween or like one or the other of the "parent" lilies.

-Helen