In computer science, soft is used to describe things that are intangible. For example, you cannot touch software. It's like music -- you can see musical scores and touch CDs and tapes, but the music itself is intangible. Similarly, you can see software instructions (programs), and touch floppy disks on which the programs are stored, but the software itself is intangible.
Soft is also used to describe things that are easily changed or impermanent. In contrast, hard is used to describe things that are immutable.