There are a few types of wood flooring to choose from.

First of all we have 20mm solid wood ,this wood can be glued direct to a timber or screed sub floor or it can be nailed down on to joists or nailed to a timber sub floor.

Then you can get a 15mm solid floor (not as common as 20mm) this can be nailed down to a timber sub floor or glued to a timber or screed sub floor , but the 15mm can't be nailed to joists as it is not thick enough to take a load inbetween the joists.

Next you get the hardwood laminate (engineered board)

This normally comes in two different thicknesses 15mm and 20mm approx .  The 15mm board has a wear layer on the top of about 3mm -3.5mm and can be botained in a 3 strip board , 2 strip board and a single plank form.This can be fitted as a floating floor on top of a quality underlay or can be glued direct to a  timber or screed sub floor.

Then the 20mm thick board has a wear layer of 6mm aprox, this board can be nailed to joists it can be nailed to a timber sub floor.This floor can also glued direct to a timber or screed subfloor or lastly it can be laid as a floating floor over a quality underlay.

Then there is parquet blocks.

There are 20mm blocks that can be glued to a screed sub floor or there are 6mm and 10mm blocks that can be glued and pinned to a timber sub floor , if these are to go over old floor boards then a suitable ply wood will need to be fitted first.

There are many species of wood to choose fron form light to dark woods.

Different size boards as in how wide and how long they are .

Some are square edged boards and some have a bevelled edge.

Some of the solid wood and some of the hard wood laminate (engineered boards) come pre finished with oil or lacquer and some come unfinished ready to be sanded and sealed on site.