COM+ is a technology stack, built approximately like this:

Buzzword Service
COM+ load balancingobject poolingIMDBMSMQeventsadministration
MTS transactionsresource poolingrole-based securityJust-In-Time Activationadministration
DCOM remote architecturedistributed component service
COM interface-based programming

DCOM failed in the marketplace, taking out most of the stack above it.

Microsoft built a monument on top of COM, a lot of which is deprecated now. This was motivated by Windows DNA, parts of which are still around.

COM+ and DNA are terms that overlap. The way I think of it is, COM+ is this specific technology stack, and DNA is more of a marketing term that means “whatever tools make up a 3-tier application”. This includes IIS and SQL Server. The list of COM+ objects is a little more tangible.