They mean that the parameters aren't tightly controlled. Look at this excerpt from a 2N2222 datasheet: 
hFE is given as only guaranteed to be a minimum value; a typical value is only given for a single test condition and it is 3 times the minimum value.
There's no good value proposition for tightly controlling these parameters, e.g. making hFE 300 +/-5% or whatever since techniques to minimize the effect of variations already exist and are in wide usage. E.g. for switching you drive it into saturation so even the minimum hFE gives way more current than you need or for amplification you design in more gain than you need and use a feedback network that is easy to design with tight tolerances to set the actual gain.