Me neither ... I'm a 48 year old Brit and both are new to me! :)

Well I can't speak for Romania, but here in France we use those units, most of the time at school, to convert one unit to another for example(Same for the weights, btw. Décagramme, hectogrammes, etc...). We also have a tool to measure length and it is called 'décamètre'.

I haven't heard of a hectometer, but I have heard of a hectare.

No, they are only used in schools, not in real life.

I reported for "millimetre, decametre, hectometre".
2017/03/05

Milli- = 1/1000; Centi- = 1/100; Deci- = 1/10; Deca- = 10; Hecto- = 100; Kilo- = 1000

One hectometer is equivalent to 100 meters. It's pretty self-explanatory.

Heck! No!

There are 100 metres in a hectometre