two by four

Short definition from Wiktionary

Noun

1. 1
   A length of sawn wood of cross section nominally 2 inches by 4 inches (actual dimensions 1½ × 3½ in modern use), most often employed as structural framing lumber (dimensional lumber).
2. 2
   A small, modest building.
3. 3
   Synonym of Tijuana Bible (“kind of pornographic comic book”).
4. 4
   Alternative spelling of two by four.

Adjective

1. 1
   Measuring two inches by four inches.
2. 2
   Small or cramped.