A novice question about 60Hz vs 50Hz frequencies in monitors
It is the screen refresh rate (approximately!). 

A little history: Way back in the day when the CRT telly was a new and shiny thing, capacitors were expensive and voltage regulators were very expensive. 
Locking the field rate of the telly cameras to the mains frequency meant that ripple on the power supply due to poor regulation and undersized filter caps in the receiver would cause brightness variations, but that they would be more or less static over time, doing anything else caused very annoying rolling brightness on the display as the supply voltage and scan position beat together.
This of course gave rise to 60Hz frame rates in the US and 50Hz just about everywhere else. 

Then colour arrived on the scene and we got another weird split, with the US slightly breaking things by going to 59.97Hz (Due to the way they decided to encode the croma subcarrier), while everyone else stayed on 50Hz. 

When computer monitors moved from expensive vector displays to use what were basically repurposed TV technology 50 and 60Hz stuck around (only now we run them non interlaced as a frame rate rather then a field rate). 

The backlights on LCD monitors do use high frequency power (If CCFL) but that is usually in the tens of KHz region, not anything that anyone is going to identify as flicker.

Modern high def telly is usually 60Hz because it really does not matter anymore, power conversion is not the costly thing it once was.