Launch means hold-down clamps releasing after engine ignition, regardless of subsequent success or failure.

"Launch" is defined as the vehicle lifting off the pad, however slightly, under thrust from its engines.

Only launches planned to be orbital or near-orbital (intended to come within ~5% of orbital velocity) count.

Relevant timezone, for determining which month a launch is in, is local time at the launch site.

Edit Nov 9th: changed the definition of "launch". It turns out that the launch clamps may be released well in advance of ignition, such that they should not be used as part of the defintion of "launch"