Original: A lay clerk, also known as a lay vicar, song man or a vicar choral, is a professional adult singer (or an accomplished amateur) in a Cathedral or (occasionally) collegiate choir in the United Kingdom.
Simplified: A lay clerk, also known as a lay vicar, is a term used in the United Kingdom to describe a male singer who sings in a cathedral choir or a choir belonging to a college of one of the large traditional universities. A lay clerk is usually paid for the job.