PER = Price/EPS.
The higher the PER, the higher the stock price compared to net profit.
A low PER means that the stock price is low compared to net profit.
There is also a strategy to invest in low PER stocks, but PER has the disadvantage of not reflecting the growth potential of a company. A low PER is not necessarily a good stock to buy. It could mean there's no growth potential and people don't expect anything.
Because PER vary so much from sector to sector, it's important to see which sector you want to invest in and to know what the average PER of other companies in the sector is.