By Definition.

ran·dom [ran-duhm]
adjective

1. proceeding, made, or occurring without definite aim, reason, or pattern: the random selection of numbers.

2. Statistics . of or characterizing a process of selection in which each item of a set has an equal probability of being chosen.

3. Building Trades .
a. (of building materials) lacking uniformity of dimensions: random shingles.
b. (of ashlar) laid without continuous courses.
c. constructed or applied without regularity: random bond.

4. Informal .
a. unknown, unidentified, or out of place: A couple of random guys showed up at the party.
b. odd and unpredictable in an amusing way: my totally random life.