Social ties that link people together with others who are primarily like them along some key dimension. For example, a group that meets of 50-year old African American men. [In reality some groups are bonding in some ways and bridging in others: for example, the Knights of Columbus is bonding with respect to religion, but bridging across social c [..]

"Based on exclusive ties of solidarity between 'people like us', exemplified by families, and is restricted to enabling people to 'get by'." (Edwards) "Bonding social capital refers to the links...

Bonding social capital is a kind of emotional support that involves making connections with other people in similar situations.  For example, people who struggle to lose weight or fight addictions often prevail because they are part of a group that helps them with these battles, such as Weight Watchers or Alcoholics Anonymous.