add network capacity

glossary.asciidoc

@@ -273,6 +273,10 @@ multisignature::
     Payment channels are always encoded as multisignature addresses requiring one signature from each peer of the payment channel.
     In the standard case of a 2 party payment channel a 2-2 multisignature address is used.
 
+network capacity::
+    Lightning network capacity is the value of bitcoin locked and circulated inside Lightning Network and is the sum of capacities of each channel.
+    It is a mesurement of the maximum value a user can transfer in Lightning Network because routing nodes will need to have sufficient balances. It also reflects the usage of Lightning Network to some extent, because the higher value is circulated inside Lightning Network the more likely that more people are using it.
+
 Noise_XK::
     The template of the Noise protocol framework to establish an authenticated and encrypted communication channel between two peers of the lightning network.
     X means that no public key needs to be known from the initiator of the connection.