Wood Floor require expansion space at the wall and all vertical obstructions. Molding are used to cover the expansion area, to hide cut ends, to adjust height differences or transitions between floors and to aesthetically finish the area. Profiles are many and vary through the industry. Here are some examples of standard profiles.

Moldings room view molding2
Baseboard From 3/8" and thicker, from 1 1/2" to 4+" high; used to protect the wall and cover expansion space
Baseshoe From 3/8" to 5/8" thick, from 1/2" to 1" high;used istead of baseboards or with baseboard to complete expantion coverage; flexible enough to conform to irregular surfaces.
Quarter Round One quarter of a dull round; from 1/2" to 1"; used as an alternative to shoe in some areas.
Reducer From 5/6" to 3/4" thicj, 1" to 3" + wide; used to make transition in thickness from wood floor down to thinner surface (or carpet or vice versa), generally through door openings. Also used to cover expansion space around vertical surfaces such as fireplace hearths when mounted directly to surface of fllooring.
Threshold/Saddle From 5/16" to 3/4", thivk, many widths; used to make the transition at doorways, between interior rooms and to the outside. Can be custom milled to any size.
Baby Threshold Often variable- used to cover expansion space in perimeter areas where vertical molding cannot be used. Example: Stone, brivk wall and hearths as well as floor to ceiling glass and sliding doors. May also be used at existing door thresholds.
Nosing Also called stair nosing,bull nose, stairwell trim,landing tread. Thickness same as flooring. Used to create finished edge on top step, around stairwell, sunken living room, etc.