$FreeBSD: head/usr.bin/top/top.local.1 237646 2012-06-27 12:30:56Z jhb $
Mem: 9220K Active, 1M Inact, 3284K Wired, 1M Cache, 2M Buf, 1320K Free Swap: 91M Total, 79M Free, 13% Inuse, 80K In, 104K Out

K: Kilobyte

M: Megabyte

G: Gigabyte

%: 1/100

Active: number of bytes active

Inact: number of bytes inactive

Wired: number of bytes wired down, including BIO-level cached file data pages

Cache: number of clean bytes caching data that are available for immediate reallocation

Buf: number of bytes used for BIO-level disk caching

Free: number of bytes free

Total: total available swap usage

Free: total free swap usage

Inuse: swap usage

In: bytes paged in from swap devices (last interval)

Out: bytes paged out to swap devices (last interval)