The release of what type of offender is frequently offered as a way to reduce the prison population?

Nonviolent offenders

Explanation:

Prison population is a major problem in most of the States' prisons. It is difficult to accommodate all the criminals in limited prison cells. Therefore release of some of the non violent offenders is an appropriate way to solve the issue.

Non violent offenders includes those crimes which does not have an actual harm or threat to any particular victim. These crimes includes burglary, tax crimes, frauds, alcohol crimes, etc. All this crimes does not involves violence and offer threat to victims.