Weak hands is a term used to describe the people who capitulated and sold their Bitcoin at the first sign of trouble. Usually people with weak hands will be severely affected by FUD and are easily manipulated off their Bitcoin position.
A lot of noobs will fit in to the category of weak hands due to not doing enough research (DYOR) and then panicking as they let their sats slip through their fingers and into the hands of those who HODL.
Sadly, those with weak hands will often sell at a loss and end up being bitter about it, sometimes converting in to nocoiners who will HFSP.
The scaling of bitcoin beyond the base chain has seen the expansion of layer two protocols, with unique trade-offs designed to facilitate a certain type