1. [from Virtual Address eXtension] The most successful minicomputer design in industry history, possibly excepting its immediate ancestor, the PDP-11. Between its release in 1978 and its eclipse by killer micros after about 1986, the VAX was probably the hacker's favorite machine of them all, esp. after the 1982 release of 4.2 BSD Unix (see BSD). Especially noted for its large, assembler-programmer-friendly instruction set — an asset that became a liability after the RISC revolution.
It is worth noting that the standard plural of VAX was ‘vaxen’ and that VAX system operators were sometimes referred to as ‘vaxherds’
2. A major brand of vacuum cleaner in Britain. Cited here because its sales pitch, “Nothing sucks like a VAX!” became a sort of battle-cry of RISC partisans. It is even sometimes claimed that DEC actually entered a cross-licensing deal with the vacuum-Vax people that allowed them to market VAX computers in the U.K. in return for not challenging the vacuum cleaner trademark in the U.S.
A rival brand actually pioneered the slogan: its original form was “Nothing sucks like Electrolux”. It has apparently become a classic example (used in advertising textbooks) of the perils of not knowing the local idiom. But in 1996, the press manager of Electrolux AB, while confirming that the company used this slogan in the late 1960s, also tells us that their marketing people were fully aware of the possible double entendre and intended it to gain attention.
And gain attention it did — the VAX-vacuum-cleaner people thought the slogan a sufficiently good idea to copy it. Several British hackers report that VAX's promotions used it in 1986--1987, and we have one report from a New Zealander that the infamous slogan surfaced there in TV ads for the product in 1992.