Lens on a board means focal length, usually millimetres (24, 35, 50, 85…). It is optional on a first-pass presentation board. It is required once a DoP is packing glass or you are promising a look to a client (“we will shoot this 35mm, not a long-lens crush”).
A wide lens in a small room is a blocking choice. A long lens is a background choice. Writing “CU” without a lens leaves that fight for the day.