五险 covers five mandatory insurances:
养老 (pension),
医疗 (medical),
失业 (unemployment),
工伤 (work injury), and
生育 (maternity).
一金 refers to
住房公积金, a housing provident fund both employer and employee pay into, which can later be withdrawn for buying a home. Having
五险一金 is shorthand for 'a real job' — job listings without it are usually informal or exploitative.