Lock-in periods are the horizon for which any investor cannot redeem their invested amount from their date of investment. 

Majority mutual funds are open ended and thus have no lock-in periods unless stated otherwise. Most popular category of MFs with a lock-in are ELSS funds that are used for tax saving purposes under 80C and have a lock-in period of 3 years.

For eg : one of the funds managed by your friend’s AMC has a lock-in of 2 years and you invest in his fund on 31st March 2021 then you will not be allowed to redeem your investment before 31st March 2023.