Nothing is more confusing, for someone not familiar with music history, than to hear about something like: "classical music".  One could define this term as:  'a  kind of art form which has proved to be of a  mature nature and balanced in emotions and formal structure.  In normal  language it  simply means that this music is not belonging to the range of easy listening or pop music. I requires a certain level of involvement of the listener.

In Western music history the term  'Classical' means the time between ca. 1760 and 1820. The period of the Viennese trinity Joseph
Haydn, Wolfgang- Amadeus Mozart and Ludwig van Beethoven.  In India  we have  the famous  Carnatic 'classic' Trinity of  Shyama Sastry, uthuswami Dikshitar and Tyagaraja.

The term 'classic' came in vogue after Beethoven's  death (1827) and denotes the perfection of form structure, the humanitarian continence and aesthetic ideals. One can freely translate 'classical' by adapting virtues as "truth, beauty, symmetry and harmony" as well as simplicity and clarity. Emotion, reason, continence and structure create a subtle balance in the outlook of the composition. You can truly say that the obtained result is 'timeless'.

For any  Asian "rasika" (music lover) who wants to know a little more about this European classical music, I give some details below:

It is obvious that one cannot draw a straight line through all these stylistic periods. All "fashions" are interwoven into each other. If you put one date earlier or later you'll be probably be right.. What matters is that one knows that from a certain "period" onwards an new concept of treating music came into being.
 

European classical music knew a evolution from monodic performance till the giant orchestras of the late 19th century. Its music evoluated to polyphony and harmony.  Instrumental performances can range from one soloist performing all alone till a 120 man orchestra accompagning one soloist.  The complexity of the music and size of the orchestras evoluated in such a way  that a additional team member was needed: the "conductor".

To perform a composition from a certain era, the musician gets, lends or purchases the score and starts working on it. To deal with the interpretation he will listen to one or more recordings of the piece and maybe read some background books  concerning the period.  He won't have to compose or add anything to it, all the necessary components of the composition are already printed. With  ancient music more research work has to be done, there one has to consult old treaties concerning the interpretations of style, rhythm, speed, embellishments etc...  For the last preparations ( in case of orchestra involvement) the soloist will study the composition together with a keyboard player,  in order to get used to the accompaniment. Finally he will get 3 or more rehearsals with orchestra and conductor before the work is performed on stage.

A Western classical concert is never performed extempore, it will be always prepared and rehearsed several days  before the concert. The percussion is never as prominent as in Indian music. To say more, in European classical music percussion has always been placed  on a side track.

The  European system tonic never changes. (this means the first sound, note of the scale (saptak) C or do (sa) will always be the same pitch) In order to perform higher or lower a other scale will be used. ( hence scales in D, E etc.)  On the Indian Subcontinent the pitch of the system tonic is changed according to the chosen instrument or voice, but still will be called "Shadja".