Mophead Hydrangea A Fast Grower?

I see it listed on Plant sites as a 'Fast Grower'. Can someone tell me what constitutes fast as opposed to slow and medium?

In the context of an ad, 'fast' can mean whatever the advertiser wants it to mean. In the context of a commercial site, it too means whatever definition they would like to apply. Some websites however, will "define" terms somewhere either on the same webpage or another one. It is nice when they clearly define terms so you know if they are exagerating.