Open Interest indicates the number of all open options contract for the particular option. This is an important measure of liquidity as it indicates the overall active participation in the position. High open interest, or high participation, in the options contract gives the trader reasonable confidence that there will be a counterparty for closing or for adjusting the position over the contract life.
The difference between the bid price and ask price which indicates how close the buyers and sellers are to an average price. Liquid stocks and options have small (tight) bid/ask spreads, which ensures good pricing and a future market to close the position.