The front month carries almost all the liquidity and the tightest bid-ask-spread. Charts and quotes usually default to it. Later months are called back months or deferred contracts.
The price difference between the front month and later months reflects carry costs and expectations; see contango and backwardation.
Example: crude oil has contracts for every month for years ahead, but on a given day 80% or more of the volume is in the front one or two months.
Related: contract-month, roll, contango, backwardation