A Chord is a Western Music concept, essentially for instrumental music rather than vocal music. A chord, when played, enhances the harmony of the musical piece.  The chords are played in a solo performance as well as in an accompaniment to vocal music/singing.
A chord is the layering of several tones played simultaneously.

To be more precise, a chord is playing of a mimimum of three different notes together. The commonest amongst the chord is a Triad
A triad  is a chord made of three notes. It consists of a root note (the first note in the sequence) and the 4th/5th note after the first and lastly the 8th note from the first.

The triads are classified broadly into major and minor chords depending upon the position of the SECOND note in the chord:
 Major Chord – 1st, 5th and 8th note and Minor chord – 1st, 4th and 8th note

For eg: 
C Major chord would involve the following notes - C F G# When translated to Indian classical music C Major would mean White 1, White 4, Black 4. If white 1 is the Shadj then this would be: S G P (Gandhar shuddha or natural) and C minor  will be -S g P (gandhar komal or minor).

 Diminished Chord and Augmented Chords – depends upon the position of the third note in the chord. Diminished Chord – 1st, 5th and 7th note and Augmented chord – 1st , 5th and 9th note
 
There are other chords like Lydian, Neapolitan, Elektra, Harmonic 7th,  Dominant Chord etc - the explanation for these would offered in a future post.
 
Playing a chord is possible on Reed instruments like Harmonium/Accordion, Piano and string instruments like a Guitar but NOT on wind instruments like Flute, Saxophone, and Clarinet etc. So what happens in these wind instruments – a chord is played as individual notes in the defined sequence, which is called  Apreggio   or broken Chord
 
Nomenclature for the chords:

The notes is the western Piano are named as C, D, E, F, G , A and B – these correspond to the white notes in the Piano. First white note in the Piano is the C, second white is D – so Safed 1 is C, safed 2 is D and so on. The Black notes are komal or teevra notes – First Black note is C sharp (C#) and second Black note is D#, 3rd Black is E#; 4th Black is A minor (Ab) and then 5th Black note is Bb
 
Chords are named from the root note. Hence they could be C, D,  E -  C Major, C Minor or D Major, D minor etc.
 
The lecture-demo clip would follow this. I have made it concise and edited it  so it is not too long.