husband's bulge
Old-timey, folksome, or religious nutjob's "polite" or naive way of explaining what a boner, visible underneath clothing is. It implies that the speaker doesn't believe sex or sexual desire should happen outside of marriage; so only a husband would have a boner. But "boner" or "erection" are too scandalous and obscene to say.
That guy in class was totally trying to hide his....husband's bulge under his books.
Husband Bulge
This expression comes from the horror movie Cabin in the Woods, released in 2011. Basically, a "husband bulge" is an erection.
"Dude, zip up your fly. I can see your husband bulge!" erection