Just learned the term: It means, to quote Black's Law Dictionary, "A pleading error or oversight that results in a misjoined issue and requires a repleader" or "The acknowledgment of such an error." It has likely remained in some use (74 Westlaw-accessible cases mention it since 2020) because of the 15th- and 16th- Statutes of Jeofails (or Statutes of Amendments and Jeofails), and later American versions of the statutes: Under those statutes, certain kinds of jeofails are not sufficient to justify vacating a judgment.

Jeofail apparently comes from the Anglo-French "jeo fail," which is to say "I am at fault," or "my bad."