Noun - prejudice in favor of or against one thing, person, or group compared with another, usually in a way considered to be unfair. (Oxford Dictionary)
Bias can manifest in many forms, and information sources can be biased. Because information is constructed, those who construct information often pass on their own biases through their work. Data can be interpreted in different ways, research studies can be set up with initial assumptions that are biased from the start, and our search engines that use algorithms, as constructions, can be biased and lead to biased outcomes. One of the best counters to bias is acknowledgement that bias exists. You can also minimize bias by using many and varied sources.
This video from NCSU Libraries shows how to determine if a source's information is trustworthy and credible.