The Hebrew word acharon (אַחֲרוֹן) means last, latter, final, or western (since west was 'behind' in Hebrew orientation). It refers to the final position in time or space and is one of the great eschatological words of the Old Testament.
Acharon gains its greatest theological force in the divine self-declaration of Isaiah 44:6 and 48:12: 'I am the first and I am the last; apart from me there is no God.' God brackets all of history — He is both rishon (first) and acharon (last). This title passes to Jesus in Revelation 1:17: 'I am the First and the Last.' The 'latter days' (acharit hayamim) — the eschatological age of fulfillment — are rooted in this same word. God holds the end as securely as He held the beginning.