means A sharp, pointed object or a sudden, steep rise (and fall) in something like a graph, signal, or measurement.

from From Middle English 'spike,' meaning a nail or pointed rod, likely borrowed from a Scandinavian source — related to Old Norse 'spik' and a whole family of Germanic words for sharp, pointy things (compare 'spoke' and the Dutch 'spijker,' a nail). The metaphorical 'spike' on a chart — a line that stabs upward — is a much later figurative leap, reading the jagged silhouette of data as a row of nails.