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A term used to describe the erectile state of a male penis in which the penis is in between being flaccid and fully erect. The term itself is a reference to a semi-hardened piece of clay.
"Every time I see a picture of Lynette Carolla, I go into the leather phase"

"What is leather phase?"

"You know... Half Mast

'Ohh, Me too"
by DJH89 March 08, 2011
Happy St. Patties Day!