What is the meaning of 大专?
Your understanding of "大专院校" is probably right.

But "大专" used alone is different from "大专院校". It is probably the short form of "大学专科", and is a kind of education after secondary schools but has shorter terms (usually 2~3 years) and does not provide a bachelor's degree. On the contrary, "大本", or "大学本科" usually takes 4~5 years and will provide a bachelor's degree.