Source : Free On-Line Dictionary of Computing

bootstrap loader
     
         (from "{bootstrap}" or "to pull oneself up
        by one's bootstraps") A short {program} that was read in from
        {card}s or {paper tape}, or {toggle}d in from the {front
        panel} switches, which read in a more complex {program} to
        which it gave control.
     
        On early computers the bootstrap loader was always very short
        (great efforts were expended on making it short in order to
        minimise the labour and chance of error involved in toggling
        it in), but was just smart enough to read in a slightly more
        complex {program} (usually from a card or {paper tape}
        reader), to which it handed control; this {program} in turn
        was smart enough to read the {application} or {operating
        system} from a {magnetic tape} drive or {disk drive}.  Thus,
        in successive steps, the {computer} "pulled itself up by its
        bootstraps" to a useful operating state.  Nowadays the
        bootstrap is usually found in {ROM} or {EPROM}, and reads the
        first stage in from a fixed location on the {disk}, called the
        "{boot block}".  When this {program} gains control, it is
        powerful enough to load the actual {OS} and hand control over
        to it.
     
        See {boot}.
     
        (27 November 1995)