A software publisher is a publishing company in the software industry between the developer and the distributor. In some companies, two or all three of these roles may be combined (and indeed, may reside in a single person, especially in the case of shareware).
Software publishers often license software from original author-developers with specific limitations, such as a time limit or geographical region for a royalty consideration. The terms of licensing vary enormously, and are typically secret.
The author-developers may use publishers to reach larger or foreign markets, or to avoid having to focus on huge initial production and marketing costs. Or publishers may use developers to create software to meet a market need that the publisher has identified.