I have noticed much confusion about terminology. Here are some definitions.
Trailer - This is an RV
Mobile Home - Home built in a factory prior to June 15, 1976
Manufactured Home - a home built in a factory after June 15, 1976
when a law requiring factory built homes be built to
HUD code took effect. They are built on a steel chassis with wheels.
Modular - i.e. "True modular" "off-frame modular"
This is a factory built home built to local code, NOT
HUD code, with NO chassis, delivered on a flat bed
and installed with a crane.
"On-frame" modular - despite it's name, it is not a true
modular. It is essentially a manufactured home with a
steel chassis built to local code.