The title is short for "Cock Blockers." Naturally, it was not called Cock Blockers because a title that vulgar would be difficult to advertise. However, a rooster (or cock) is shown before the word "Blockers" to hint at the full title.
This film was produced by Evan Goldberg and Seth Rogen, the creators of "Superbad." "Superbad" is a film about three high-school friends who try to have sex before graduation. A very similar story to "Blockers," except "Superbad" features male protagonists rather than female.
The trivia items below may give away important plot points.
Early on in the film, Hunter (Ike Barinholtz) makes a joke about his daughter Sam (Gideon Adlon) watching "Asian porn" like he does. It is soon revealed that Sam is indeed attracted to an Asian girl, Angelica.