Rebalance means revert back to initial allocation %. For eg: if you have 1L and want to equally allocate it to 5 strategies then each strategy will get 1L/5 = 20K.
After one month the allocation % will change due to the market dynamics..and the new allocation could be 15K, 25K, 30K, 20K& 35K, then to rebalance it we need to find the total value and divide by 5, 15+25+30+20+35 = 125K/5 = 25K each. This way for the next month your new rebalanced strategy will get 25K each.