Use a forward slash (or stroke) as a substitute for or with no space on either side, except when either of the separated items themselves include spaces.
- male/female
- Y/N
- n/a
- names and titles / words and spelling
- lecturer / senior lecturer / associate professor / professor
When writing for the web
Online, the spaces on either side of the slash can be omitted or inserted as needed to avoid unintentional/misleading line breaks.