In economics, what is it called when reduced demand cause prices to go up?

The well-known idea of supply and demand tells us that prices are likely to go up when there is a limited supply and an increase in demand. This question deals with the opposite case, when prices are high when there is a low demand.

In the field of software development, there is only the one-time cost of developing the software. Once the software is developed, an unlimited number of copies can be made.

Finale and Sibelius are competing companies in the music composition software business. Both of their main products cost around $600. Microsoft has a near-monopoly on operating systems, yet its main product (Windows 7 professional) costs $200. As far as I can tell, windows probably spends a lot more money on software development (per each piece of software) than Finale, but most of it’s products are cheaper.

I think that I understand the general reason for this- when a company sells fewer copies, it has to raise the price to make more money off of each copy. The opposite strategy is to lower the price to attract more buyers.

What is this phenomenon called, and when does it occur?