What is "thick as a brick"

a. (context simile English) stupid; slow to learn or understand.

Thick as a Brick is the fifth studio album by the British rock band Jethro Tull, released in 1972. The album is notable for only including one song, which spans the entire album. Thick as a Brick was deliberately crafted in the style of a concept album, as well as a "bombastic" and "over the top" parody of the then-prevalent vogue for concept albums. The original packaging, designed like a newspaper, claims the album to be a musical adaptation of an epic poem by the fictional 8-year-old genius Gerald Bostock, though the lyrics were actually written by the band's frontman, Ian Anderson.

The album was recorded in about three weeks in December 1971, featuring music composed by Anderson and arranged with the contribution of all band members. The live show of 1972 included the playing of the full suite, with various comic interruptions. Thick as a Brick is considered by critics the first release by Jethro Tull entirely consisting of progressive rock music and received mixed reviews upon its release. Nonetheless, it was a commercial success and topped various charts in 1972. Today it is regarded as a classic of progressive rock and received several accolades. Ian Anderson produced a follow-up to the album in 2012, focused on the adult life of Gerald Bostock.