Split
This Node can be used to split an input into up to four outputs. The output values will depend on the input node assigned, although you can set a single input value in the Inspector window if required:
The available option is:

x
This permits you to set a single input value instead of using an input node. This value will be cast as a Vec4 before the components of the vector are output as individual floats, where the first value of the vec will be the "x" value, and all others will be 0.
Node Outputs
This node has four seperate outputs, each of which are a float. The values being output will depend on the input itself, which can be a single float, a vec2, a vec3 or a vec4. The outputs will be ordered as x/y/z/w from top to bottom:
Here each output value is a component of the input. If the input is not a vec4 then it will be cast as a vec4 to generate the required 4 output components, where each "empty" value will be output as 0. For example, a vec2 input (32.0, 56.5) would output x(32.0), y(56.5), z(0), w(0). Note that you don't have to use all outputs and can use any of them in any order.