Net exposure = longs - shorts, usually stated as a percentage of equity. $60,000 long and $40,000 short on a $50,000 account is +40% net: you are modestly long.
Net is the number that tracks with the index. A +40% net book roughly captures 40% of a market move, before differences in beta between the longs and shorts - which is why serious desks use beta-weighted-delta rather than raw dollar net.
A low net is not a low risk. Net exposure can be near zero while gross-exposure and single-name risk are enormous, and paired trades unwind violently when a merger breaks or a sector rotates. Zero net protects you from direction, not from being wrong about relative value.
Related: gross-exposure, beta-weighted-delta, long-short-ratio, hedge