The words "transition strip" -- also sometimes called a threshold -- refer to the strip of flooring material that is placed between two rooms. Transition strips are not meant to be a divider but to provide a transition between two rooms that meet at an entry point.
Transition strips can also be used in the doorway where a room meets a hall.
Different Floor Materials
Use transition strips when two different flooring materials meet in a doorway. For example, a hardwood floor that runs up against a linoleum flooring material needs a transition strip.
In this case, a transition strip hides any irregular edges between the hardwood and the linoleum so that the edges between the two materials appear to be even and straight.
Same Flooring Material
Sometimes doorways have a rough transition between rooms, even if the same flooring material is used in both rooms. For example, in the case of a hardwood floor, there often are nails embedded in the doorway.
To prevent people from hurting themselves or tearing their socks on the nail heads, a transition strip is nailed down between the two rooms to cover the nails.
Some transition strips are meant to lie between two floors that aren't level with each other. When areas of flooring are very far apart from each other, a step is made.
In the case of floors that are only half an inch or an inch apart, a special transition strip called a "reducer" is used. The reducer smooths the transition between the higher floor and the lower floor.
What Type of Strip
Transition strips come in different materials. Most common are metal and wood.
Wooden transition strips are used when a hardwood floor meets another material or another hardwood floor. Wooden transition strips should be stained to match the wood on the floor.
Metal transition strips are common when carpet meets linoleum and when carpet meets hardwood.