yes, but there is a difference between mashing and steeping: the grains you use.
you need grains that have diastatic power. if you look at the grains at briess you will see the DP 140 on 2-row
and you see that specialty malts
, crystal malts, etc. do not have any diastatic power. basically, they do not contain enzymes and in turn cannot convert starches into sugars.
so, if you have grains included in your mash that have diastatic power, you are in fact doing a mash. if you are just using crystal malts, you are steeping.
it also depends on the amount of water you use. you can steep in a larger amount of water, but for mashing you want somewhere between 1-2 quarts of water per pound of grains.
i generally use 1.25 quart per pound when i do all grain. it gets a bit thinner with this method.
that being said, i still use a small amount of water at 155°F, even when i do a simple steep.