A shadowban is the widely used term for a sudden, unexplained drop in an account's reach or discoverability that the platform never formally announces — posts stop appearing in hashtag results or on discovery feeds, and reach falls off a cliff. Platforms rarely confirm the term, but they do reduce distribution for content that brushes up against their guidelines.
It matters because it can quietly kill a channel's growth. The usual triggers are borderline or flagged content, banned or spammy hashtags, bot-like behaviour such as mass following, repetitive posting, or repeated community-guideline strikes.
To recover, pause posting for a day or two, delete any recently flagged posts, drop suspicious hashtags, and stop automation that looks like spam. Long-term, stay well clear of policy edges and vary your content and tags. Before assuming a shadowban, rule out the simpler explanation: a normal algorithmic dip or a weak run of posts.