Originally, plywood referred to wood panels made of multi-layered veneer, bonded together with glue. 
While this term is still accurate, today the name plywood has become more generic, being used to refer to all types of engineered wood panels.

Below listing are the various types of plywood that are currently available on the market and their uses:

Softwood Plywood
This is the most common plywood product, made of softwood veneer, usually fir. The layers are stacked at a right angle to each other and glued together with resinous glues. Softwood plywood usually comes in 4’ x 8’ sheets, although 5’ x 5’ sheets are also available. A large number of grades are available, depending upon the intended application. 
Softwood plywood is used most commonly in the building trades for wall and roof sheathing and for sub-floors. It is also used in construction of crates and boxes. Due to its ready availability, softwood plywood is an excellent choice for home building and do-it-yourselfers.

Hardwood Plywood
Most commonly used for cabinet and furniture 
making where a smooth, attractive surface is required for finishing. Hardwood plywood is manufactured the same as softwood plywood, except the exterior layers (face and reverse) are made of hardwood. Common hardwood plywood available includes: alder, oak, red oak, birch, maple, and mahogany. It is typically AB grade plywood.

Medium Density Fiberboard (MDF)
MDF differs from particle board in that it is created from individual wood fibers, instead of sawdust and wood chips. This creates an extremely flat board (flatter than softwood plywood made from veneers) consistent in material thickness and density, with no voids. Due to its very smooth finish, MDF is excellent for painting or vinyl veneer coating. MDF is slightly stronger than particle board. 
It has the greatest weight when comparing to other types. 

Medium Density Hybrid (MXB)
MDX is a combination core of veneer core center between two layers of MDF. MXB panels have a better surface quality than panels constructed with rougher softwood or hardwood cross bands and provides a strong, smooth building material but not as heavy as regular MDF.

Particle Board
Particle board is made of sawdust, shavings and tiny pieces of wood which are mixed with glue and pressed into sheets. It is the most economical, but the weakest of all sheet goods. Particle board is commonly used under laminates on counter tops and for shelving. Most inexpensive furniture uses vinyl covered particle board for large surfaces, usually trimmed with solid wood.

Marine Plywood
Designed for use in the construction of boats, marine plywood is specially treated to resist rotting in high-moisture environments. Marine plywood is manufactured with no core gap caused by cracks or knotholes, to prevent water 
from becoming trapped in those voids. Water boiled proof glue, similar to what is used on exterior plywood is used to bond the layers together. This feature certainly affects the price. Marine plywood costs about three times the cost of standard plywood

Oriented Strandboard (OSB)
While most people see OSB as being an inferior product to plywood, building codes recognize it as being an equivalent material. Instead of being made of wood veneers, OSB is manufactured from wood chips or strands, creating about 50 layers in the average sheet, as compared to 5 or 7 in softwood plywood.  It costs about 20 to 30 percent less than a comparable thickness sheet of softwood plywood. OSB is commonly used in construction, for sheathing, roof decking 
and sub-flooring. OSB is available in sheets up to 24 feet long.