One definition you can read is from http://www.investopedia.com/university/value-investing/value-investing1.asp
If this applies to businesses or stocks, it's about buying businesses or stocks (or shares) at a sensible price or when they are undervalued.
"Price is what you pay, value is what you get." - Warren Buffet
Mr Warren is one of the present day value investors, making tons of money investing in good, unvalued business. In the 80s, he did lose a significant amount of money on airlines' stocks. Only recently, he started buying them again, this led to airlines stocks going up and up, and others are following him.
http://www.forbes.com/sites/antoinegara/2016/11/14/warren-buffett-comes-around-on-airlines-after-calling-them-a-death-trap-for-investors/#14f5d7f569d7
Recently, I read a book by Joe Geenblatt, it's called 'The little book that still beats the market'. it's a good read for anyone interested in hassle free investing into good US stocks. The book is really about using his magic formula (https://www.magicformulainvesting.com/Screening/StockScreening) to automatically select 30 to 50 stocks, depending on the market capitalisation, and then you invest in them. Caveat though, it's not meant for short term investing, but for at least 5 to 10 years or even longer. Joe claimed that by the end of the term, the returns would be more than what you get if you invest in S&P 500. If you are interested, read the book first, understand how the stocks are being chosen, then go to his magic formula site, register an ID, login and MAGIC!
