Definition
The default weather minimums a pilot must use when planning an alternate airport on an IFR flight plan, in the absence of a published alternate minimum for that airport. For an airport with at least one precision approach, the forecast weather at the alternate's estimated time of arrival must be at or above 600-foot ceiling and 2 statute miles visibility. For an airport with only non-precision approaches, the requirement is 800-foot ceiling and 2 statute miles visibility.
Plain English
When you list a backup airport on your IFR flight plan, the forecast weather there has to be good enough by these standard numbers. If the backup has a precision approach, the forecast must show clouds at least 600 feet up and visibility of at least 2 miles. If only non-precision approaches are available, you need at least 800 feet of cloud clearance and 2 miles of visibility.
Context Anchor
You encounter this when planning an IFR flight and deciding whether a listed alternate airport legally meets the required forecast weather.
Derivation
"Standard" here means the default rule that applies whenever the FAA has not published something different for a specific airport. "Alternate" comes from Latin alternare, meaning to take turns -- the alternate airport is the one you take turns to if the destination doesn't work out.
Why Pilots Care
Guarantees a usable backup airport with sufficient weather to complete the flight safely if the destination becomes unavailable.
Intuition Check
Do not read “standard” as meaning “always use these numbers.” Use the standard 600-2 or 800-2 values only when no different alternate minimums are published for that airport. Do not confuse alternate minimums with the landing minimums used when actually flying an approach. Alternate minimums are for planning whether the airport is acceptable as your backup.
Example Sentence 1
The forecast for the alternate showed a 700-foot ceiling and 3 miles visibility, so it met standard IFR alternate minimums for an airport with a precision approach.
Example Sentence 2
Because the approach plate listed 800-foot alternate minimums, we could not use the standard 600-and-2 values.