An income investor is one who invests in order to generate an income, rather than for capital gains as a growth investor would. An income investor would usually invest in bonds, high yield shares and bond like securities such as prefs.
The typical income investor is someone who depends on their investments for income, and therefore they generally tend to be conservative and buy low risk investments. However, most investors who are willing to take some risk for a higher income — otherwise they would not invest in anything other than index linked gilts!
In the case of shares, income investors will often pick the same investments as value investors. This is because dividend levels are usually set at levels a company feels confident it can maintain. So dividends are related to conservative expectations about short term profitability. This means that high yields are a positive signal for value investors.
However, income investors should not only look at these measures. They will usually need to at least preserve their capital, and they should therefore also look at the measures a growth investor would use; they need to be aware of value traps.