From the Washington Times article:
"At issue is the notion of what constitutes a "recess" appointment. Presidents have the absolute authority to make recess appointments without Senate approval. Those appointments are temporary. Recess appointments are never popular, but they are legal. This is not in dispute. The situation becomes murky when the Senate holds "pro-forma" sessions.
A pro-forma session in recent years has involved the Senate opening for as little as thirty seconds where one person shows up and bangs a gavel. In other words, even though little to no work is done at many of these sessions, it counts as an actual session. This is designed specifically to avoid being categorized as a recess, even if most members are gone for several weeks.
President Obama argued that these pro-forma sessions were a complete sham. On this issue, he is right. They violate the spirit of the law."