Hi,
The datasheet for the LM334 is an example of an IC current source. You can make current sources many ways, using op amps, or transistors, some circuits use a BJT, a diode or an LED and a few resistors, look at Wikipedia's "Current source" page, for example.
A resistor in series in a circuit draws current, so surely it is a (current) load, not a current source.
TO my understanding, a current source is a constant, reliable and known quantity of current. LED drivers use constant current sources if I'm not mistaken.
If you bias the base of a BJT to "1/10th" of the collector current required, e.g. collector current 1mA so bias base current to 100uA, more or less you get a constant current source, which will vary a little with temperature or if you alter the supply voltage.
Voltage reference ICs can be configured as current sources, so can some temperature sensors as they are all "basically" a diode.
One practical use for a current source is an Ohmmeter, and internally a lot of ICs have sections which depend on current sources, for example Op Amps.