There are several definitions, and even within those defs it's still open to subjectivity:
- Pre-installed software that's not required by the OS to work
- Redundant or duplicate apps installed on a device
- Undesirable programs that were never requested by the user
- Software that has become bloated over time
This is a problem because most bloatware tends to be pre-installed because the device manufacturer (OEM) has a contract or partnership with another corporation who's interested in "getting exposure" (actually, to advertise itself and collect user data) [citation needed].