On the hike to Sparrowhawk Tarns, we encountered a very short section of rock that required us to use our hands. The question arose of whether it was scrambling or not. My answer was, "That depends. If the thought of scrambling scares you, no. If the thought of scrambling doesn't scare you, yes."
Although I'm sure my answer didn't instill confidence in my qualifications to be leading a hike, it's the best I could do. Ask 100 scramblers for a definition of when steep hiking turns into scrambling, and you'll get 100 different answers. While most of us can identify a moderate or difficult scramble when we see it (considerations include how often you have to use your hands, if you fall whether you'll get hurt bad, get hurt real bad or get so hurt you'll be dead) you'll find considerable disagreement over what constitutes an easy scramble.
In his book Scrambles in the Canadian Rockies, Alan Kane defines an easy scramble as "easy hiking, much hands in pockets stuff, little exposure, no maintained trail. Not surprisingly, easy scrambles are not really scrambling at all but are mostly off-trail hiking."
Although Kane's easy, moderate and difficult ratings don't exactly follow the UIAA or YDS ratings, they're the most useful if only because you can actually make sense of them (apologies to the UIAA and good people of Yosemite). Back in the day when I was a but a kid trudging up Heart Mountain in running shoes and blue jeans, most of the things we call scrambles today were called steep hikes. In fact, there was only hiking and climbing. Need to use your hands? Steep hiking. Need to use a rope? Climbing. It was simple.
All too often, I hear people say they'd like to try scrambling but aren't sure if they're ready. Don't let the word "scramble" intimidate you. If you can do a hike with significant elevation gain, you can do an easy scramble. Then go to work on Monday, tell everybody what you did on the weekend, and figure out for yourself how to explain what a scramble is.