To put or insert something into something else, such as an appliance, structure, vehicle, etc. A noun or pronoun can be used between "load" and "in." Let me know when you're finished loading that timber in. I can't believe it—I loaded in all the clothes but forgot to turn on the washing machine!
See also: load
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.