Definition:
A go-to-market strategy (GTM strategy) is an action plan that specifies how a company will reach target customers and achieve competitive advantage. The purpose of a GTM strategy is to provide a blueprint for delivering a product or service to the end customer, taking into account such factors as pricing and distribution. A GTM strategy is somewhat similar to a business plan, although the latter is broader in scope and considers such factors as funding.
Further Reading:
Book: The Lean Machine by Dantar P. Oosterwal.