A Market is “various groups of customers.”
Marketing Management, 15th. Edition, Philip Kotler, Kevin Lane Keller.

A market should be described in terms of customer need and in a way that covers the aggregation of all the alternative solutions that customers regard as being capable of satisfying that same need.
Adapted from Marketing A Complete Guide, Malcolm McDonald, Martin Christopher.

A Market is:
· a set of actual or potential customers,
· for a given set of solutions,
· who have a common set of Jobs To Be Done, and
· who reference each other when making a buying decision.
Adapted from Crossing The Chasm, 3rd. Edition, P35, Geoffrey A. Moore.

For example, some who makes buttons should think more broadly than simply a market for all the various types of buttons, but should instead consider all the alternatives to buttons for the fastening of things such as clothes. With a broader view, products such as Velcro and zips become seen as alternatives and competitive offerings.