ms is a unit of time:
ms = milliseconds,
1 ms = 0.001 seconds = 1000th of a second.
1000 ms = 1 second
While hours, minutes and seconds usually suffice for us, electronic times go in milli [10^-3], micro [10^-6], nano [10^-9], pico [10^-12] etc. seconds.
The larger the ms you see while tracing, the more time is consumed for the packet to traverse that link.
Thanks.