All Hindu gods have some asthras with them. In that the most important one of Lord Muruga is the "VEL", which is also called as Velayutham. Vel is the true representation of Lord Muruga.
True meaning of vel:
Actually Vel is in a contour of sharp edge, wide upper part and very depth in its length. This expansion, the breadth, the width actually represents the broadness of the mind. The sharp pointed end represents the sharpness of knowledge. The length depicts the Depth of our thought and mind
Thats why among hindus many people are having their names as vel, velayutham etc.... which really means a very intelligent talented person. No one'll like to have their name as the name of some weapon. So it actually refers Lord Muruga and his wisdom of knowledge.
Lord is full of wisdom.
Vel as Asthra and Sasthra:
Among Hindu Gods some have asthram and some have sasthram. But the speciality of Vel is it is used as both asthram as well as sasthram.
The Asthras are the ones which are released from the hand.
The Sasthras are hand held fighting equipments.