LND describegraph and getnetworkinfo RPC response
After looking into the code and running some tests I think I've found the answers:


avg_out_degree is the average channels per node. In other words, total channels / total nodes = avg_out_degree. source
max_out_degree is the maximum channels (sum of incoming and outgoing) found on a node in the network. This can be found by iterating through every node and summing their incoming/outgoing channels to find the maximum. source
time_lock_delta: the required timelock delta for HTLCs forwarded over the channel. source
min_htlc: the minimum value in millisatoshi required for incoming HTLCs on the channel. source
fee_base_msat: the base fee charged regardless of the number of milli-satoshis sent. source
fee_rate_milli_msat: the effective fee rate in milli-satoshis. The precision of this value goes up to 6 decimal places, so 1e-6. source