How does hiking differ from trekking?

hi!
I am a new comer here. I've been wondering what's the difference between hiking and trekking? What exactly do they mean? Is there any rating and grading system for each of them? Is it related to trail difficulty, elevation, weather,climate, surrounding, time of hiking and pack weight?
Does any one know about this? Since hiking is still a novel ourdoor activity in my country so I think it may be better defined where it is better and longer developed.
Thank you very much!

[pedxing]

I don't believe there is a technical definition apart from the dictionary definition. In my usage, hike is a fairly general term (but it implies one day unless the context suggests otherwise) and a trek is a longer and more difficult trip than a "mere hike."

I'll be interested to see how others define it.

[Greg]

I would say backpacking and trekking are synonyms, with hiking being a more general term which includes dayhikes.

Call it whatever you want, just get out and do it...

[Mike P.]

The terms can be interchangable but with our world shrinking thanks to jet travel, the www & the need to plan the ultimate vacation, trekking has been used by companies selling you adventure travel.

People Trek to Everest Base Camp, You can trek in the Andes, Patagonia, The Canadian Rockies & other places in the Himalaya & the Alps. (In Europe (I forgotten the eaxact word but it's looks like its based on our word wandering) In society groups organizing Treks don't sell groups on hard summits in faraway lands, people may not carry much of their overnight gear or food, it may be carried by porters, Yaks, Llamas, mules, ox. alpacca, etc. In the Himalaya, while you may have porters, your group would not require a climbing sirdar & may not have Sherpa guides as you see them refered to in the tales from Everest. Trekkers may due to walking but they may not carry their own equipment, they might though. Backpacking by definition means that you carry all your gear on your back.

[Geo.]

Trek is derived from a South African word, and generally implies a group of people mirating with their belongings as apart from, say one or two persons just, 'hiking'.
I think it's come to be used in the sense of a group of people, more often with guides or with porters, or with animal transport (eg camel trek) hiking for any distance, whether short duration or long.
You might be interested in my trek from Mexico to Canada (little plug for my website here )
whereby I was the only porter, and the camel!
http://www.angelfire.com/trek/nz_usa
Thing is, as has been mentioned in another reply, it doesn't really matter what it's called, just have a crack at it!
Cheers, Geo.