An all-time high (ATH) is the highest price an asset has ever reached. The market watches it closely, partly because at a new ATH every holder is, on paper, in profit — there is no overhang of underwater buyers waiting to sell at break-even.
A common mistake is to treat a price far below its ATH as automatically cheap. The previous high may have been an unsustainable spike, and plenty of assets — especially speculative coins — never reclaim their peak. The old high is history, not a target the price is owed.
ATHs attract attention and headlines, which can itself fuel momentum in both directions. Useful as a reference point for where an asset has been, an ATH says nothing reliable about where it is going next.
Worked example
A coin trading 70% below its all-time high is not necessarily "cheap" — that peak may simply never return.
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This definition is general education, not investment advice. Markets — especially crypto — are volatile and you can lose money. Please read our disclaimer and see our methodology.