BGP MED
Multi-Exit Discriminator — a BGP attribute that suggests to a neighboring AS which of several entry points it should use to reach you. Lower MED is preferred. A (weak) way to influence INBOUND traffic, unlike local-pref which steers outbound.
Use case: your AS has two links to the same neighboring AS (e.g. one in the north, one in the south). By advertising different MED values for different prefixes you can suggest "reach this network via the northern link, the other via the southern" → influencing where the neighbor sends traffic in. Weakness: MED is a SUGGESTION — the neighbor can ignore it, and it's normally only compared between routes from the same neighboring AS. It also comes far down in BGP's decision process (after local-pref and AS-path), so it's a blunt tool. Steering inbound traffic is generally hard in BGP (you don't control others' decisions) → MED, AS-path prepending, and more-specific advertisements are the limited tools you have. Related to BGP local-pref and BGP communities.