What is meant by AutoCAD mechanical? is it different from general AutoCAD?

AutoCad is a Computer Aided Design or Drafting in which u can draw mechanical, Architecture and Electrical Design.

Yes they are different. AutoCAD Mechanical includes all the functionality of AutoCAD, plus libraries of standards-based parts and dedicated functionality suitable for mechanical CAD design.

Most of the portion is same. 

 

Mechanical is more specific to Mechanical Industry esp with library of piping, bolt screws etc.

 

AutoCAD general can be used for any industry. Not customized.

AutoCad has laid out it's programs to cater for Mechanical Drafting ... Civil Engineering ... Architectural ... just to name a few. 

Each program has icons which are more utilized (customized to a specific task) ...

My instructor commanded the Civil Engineering program, since in his opion you can work more than in just one field.

AutoCad General - is a program which let you draw for any industry and and is not customized for any Engineering field 

it's the same but it includes standard parts as shafts, rivets or I sections and in the3d sections you can make3d models of mechanical parts

AutoCAD mechanical have few addition options for tolerance, fits. More over you can import standard bolts, nuts, etc.. depending on the standards.

The most important mechanical properties of concrete are:

Pore Size and PorosityDrying Shrinkage and CreepCompressive StrengthSplitting Tensile StrengthFlexural/Bending Strength

 

Autocad mechanical is a design and drafting software for automating mechanical CAD  task

Autodesk have special versions of can which are customised with special lisb and library to get the best use for each trade

They both are darfting and desiging softwares having said that they AutoCAD & AutoCAD Mechanical are two different "softwares" with same purpose, as every software which has a prefix of AutoCAD.
The AutoCAD software is for general use every draftsman of any field can use it but the AutoCAD Mechanical is specifically for mechanical draftsman specially for those who make darwings of machines, Spare parts, piping etc.
Now the difference is in the tool palletes and block and commands but the user interface is same.
For more difference see the below links.
features of AutoCAD mechanical : http://www.autodesk.com/products/autodesk-autocad-mechanical/features now if you see the above link one can clearly see the difference as the features in AutoCAD Mechanical are not in general purpose AutoCAD.
I hope this satisfies you.

Autocad design is generally used for basic design as the architect and the planning of large-scale images. 

Autocad mechanical working drawings for automotive engine or associated with heavy equipment