The term “lamdan” is used in different ways. The typical “yeshivishe” usage is the for word “lamdan” to be used in contrast to the term “talmid chacham”. “Lamdan” refers to someone who is able to make fine distinctions within a sugya, with deep analysis. Think R’ Chaim Brisker, The Brisker Rov, R’ Shimon Shkop.
“Talmid chacham” is used to describe someone with a large breadth of Torah knowledge, also referred to as “b’kius”. The two are not necessarily mutually exclusive, but some excel in one area more than the other.
The term used for someone who spends a lot of time learning, and/or whose learning is focused, is “masmid”.