if your referring to those who hop every 6 months, then they can be called leaping frog without proper specialization.

every 4-5 years is the ideal case for <40 years old or so. Say your current job grade is lvl5, and you know it takes ~5 years to level up. You can hop to another RELEVANT company to receive that higher job grade + salary markup + new experience. And when time comes, you may opt to hop back to your original company, and the "old" workers will realise how you manage to be in so much higher grade than them in the same time window. Its pretty common, like example my CEO is only 40 years old, numerous experience in all other competitor companies and had experienced in my(his original) company years back. The added value in him is high. Its a huge O&G mnc btw.