Number is the posting key every voucher leg, rule and report references — stable, and the reason the chart is a fixed value rather than a table anybody can edit. It looks numeric and is a string: "1000" sorts and compares as text.
Party marks the account as carrying a SUBLEDGER — receivable is money owed to us, payable money we owe — so a leg posted here also writes a payment-ledger row against a counterparty. Absent means no subledger: a bank, wallet, revenue or cost account tracks no counterparty at all.
Type is the account's fundamental class, which is also its NORMAL balance side: asset and expense are debit-normal, liability, income and equity credit-normal.