We should drop the use of the word tetrad or at least learn what its area is!

The word tetrad is used to describe a square area of land with sides of 2km it has an area of 4km². The term tetrad is widely used in biological recording in the UK, but it often misunderstood both in the UK and abroad. Logically it is derived from the ancient Greek word for four. Likewise a monad has 1km sides and has an area of 1km² . A pentad and a hectad have sides of 5km and 10km respectively, but they have areas of 25km² and 100km² so their name is based on the length of the side not their area. Outside the UK many people assume a tetrad has sides of 4km, because this follows logically, but lack of a logical series is perhaps why there are so many mistakes.

Mistakes are not hard to find, below are some examples published in official publications where the area of a tetrad is wrong...

• In the journal PLOS One
• Among mammal recorders
• By the British Trust for Ornithology
• By the Royal Society for the Protection of Birds
• By other birdwatchers
• By the Joint Nature Conservation Committee 
• By a Wildlife Trust
• By a County Council

Perhaps it is time to drop the use of this ambiguous term!