A Professor is an academic  an academic rank at universities and other post-secondary education  institution
How are professors different from teachers at k-12?
Yes they are, the name was derived from Latin as a "person who professes" being usually an expert in arts or sciences
So professors must have more education than teachers.  Do professors have an opportunity to advance?
Professor
Professor (commonly abbreviated as Prof.) is an academic rank at universities and other post-secondary education and research institutions in most countries. Literally, "professor" derives from Latin as a "person who professes" being usually an expert in arts or sciences, a teacher of the highest rank.
In most systems of academic ranks the word "Professor" only refers to the most senior academic position, sometimes informally known as "full professor". In some countries or institutions, the word "professor"
A university must have a certain number of professors and docents among its staff to receive accreditation for its study programs, but these need not necessarily be heads of departments or university faculties.
According to the Higher Education Act, No. 111/1998 Col. the nominee’s qualifications are assessed by at least five professors, specialists in the field or a field similar to the field in which the nominee is to be pronounced a professor. At least three of these professors must be from universities other than the nominee's one. An