This is the 523rd most frequent Finnish word.
metriä
The Finnish word "metriä" means "meters" (partitive case of "metri").
Here, 'metriä' is the partitive case of 'metri', used because 'kahden' ('of two') typically requires the partitive case to indicate an amount.
Pidän kahden metrin etäisyyttä muihin ihmisiin.
I keep a distance of two meters from other people.
In this sentence, 'metriä' is used with a comparative expression (pitempi, 'longer'), and the partitive case fits describing a quantity yet to be exceeded.
Jokainen metriä pitempi askel oli huomattava.
Every step longer than a meter was noticeable.
Here, 'metriä' is used in the partitive case to describe a measurement of distance being covered or involved in the action of running.