"Meristem- specialized region of cell division where growth is restricted." Is this statement correct. I dont think so because in meristems region there the cells divide actively. Is this is statement correct?

This statement is correct. However, the framing of sentence looks confusing. 
The proper way of writing this sentence would be 
In plants, the growth is largely restricted to specialized regions of active cell division called meristem.

This means that growth in plants mostly occurs in the region of meristem because it contains actively dividing cells.