H.O. 

1) A specific type of model electric train. Known both as H.O. scale and H.O. gauge. The letters come from "Half-O", since H.O. was originally half the size of an O gauge train. The scale of H.O. is 1/67, and its gauge is 16.5mm. H.O. trains are the most popular size in the world.

2) the scale of H.O. trains, which is 1/87. It can eb applied to trains, minitaure figures, or model kits.

1) Jimmy has a set of H.O. trains running in his basement.

The Hobby Shop carries H.O. trains

2) Are those model plains 1/72 or H.O. scale?

This diorama is done to a precise H.O. scale.

H.O. by Tom from the Shore December 12, 2007

h.o. 

an abbreviation for hold on

cutegirl101-can u h.o. 4 like 1 sec??
hotness123-ok
(in a chatroom)

h.o. by hvjvfhj,hcyhvcjlvchyk August 22, 2008

H.O. 

A hard on
A Hard one
a guy that has a hard penis
a guy that pops a boner

"Sheez...Stacey when i talk to you i get an H.O." -J.R.

H.O. by Boobie Trap October 27, 2005

h/o 

h/o is an abbreviated way of saying "hang on."

Can I read you my story really quick?

Sure, but h/o a sec

h/o by Gyrapage May 3, 2005

H/O 

Honest Opinion. Often used on sites such as ask.fm to ask for a person's opinion of someone

Question: "H/O on Sera"
Answer: "She's a bitch"

H/O by ravix84 January 24, 2015

h/o 

Abbreviation for "highest offer"

The h/o for the painting is $250.

h/o by Oragutang August 15, 2007

h.o 

Abreviation Used in internet language meaning Hold on

Guy:"Hey can you tell what was todays homework?"
Girl:"h.o"
Guy: "ok"

h.o by Keanu!!!! December 5, 2007