Inactive Channel

An inactive Lightning channel is one that hasn't routed any payments recently. How long counts as "recently" is up to each node operator; there's no fixed cutoff. Node software also uses the word in a narrower sense. In LND, for example, a channel is inactive when the peer on the other end has gone offline, and after a short wait the node tells the rest of the network that the channel is disabled.

Inactivity isn't a problem in itself. A channel that's just sitting there, perfectly balanced and not being used, isn't doing harm. It's just... not being useful, either. The capital is locked up in 2-of-2 multisig, paying opportunity cost.

Why operators care about inactive channels:

• Capital efficiency. A routing node might have 100 BTC distributed across 50 channels, 20 of which haven't moved a sat in months. That capital could be redeployed.
• Offline peers. If the peer has gone offline for good, the money in the channel can only come back through a force close, which keeps it locked up for a while longer.

What operators do with inactive channels:

• Close them to free the BTC for redeployment.
• Rebalance them via circular payments or splicing - sometimes inactivity is a side effect of being fully depleted on one side, and rebalancing brings them back to useful.
• Give private channels more time. A private channel to a mobile wallet or a payment-only node can sit idle for long stretches and still be worth keeping, because payments from that peer have a good chance of going through you. Whether a channel is private is settled when it opens, though. A public channel can't be switched to private later; the only way is to close it and open a new one.
• Just leave them alone if the cost of closing exceeds the value of recovering the capital.

Some mobile wallets manage channels for the user (Phoenix is one), so you may never see an inactive channel as a concept. For routing-node operators, channel activity is worth watching, and managing inactive channels is part of the operational work. Tools such as Lightning Labs' Faraday report how much each channel has routed, to help spot the ones that aren't earning.