Total addressable market (TAM) is a term that is typically used to reference the revenue

Revenue

In business, revenue is income that a company receives from its normal business activities, usually from the sale of goods and services to customers. In many countries, such as the United Kingdom, revenue is referred to as turnover....

 opportunity available for a product or service. TAMs help to prioritize business opportunities

Business opportunity

A business opportunity involves the sale or lease of any product, service, equipment, etc. that will enable the purchaser-licensee to begin a business. The licensor or seller of a business opportunity usually declares that it will secure or assist the buyer in finding a suitable location or...

 by serving as a quick metric

Metric (mathematics)

In mathematics, a metric or distance function is a function which defines a distance between elements of a set. A set with a metric is called a metric space. A metric induces a topology on a set but not all topologies can be generated by a metric...

of the underlying potential of a given opportunity.

One approach is to estimate how much of the market you can gain if there were no competitors. A variation is to assume no competition and total product distribution. This provides a focus on the user needs you can meet. Including competition and distribution issues would be something close to a forecast.