S-Parameters, Smith Chart, and Reflection Coefficients
N-port systems have N^2 S-parameters, so yes, 1-Port has 1-S-Parameter (which is called reflection factor).
Here’s an explanation attempt for S-Parameters: When dealing with conductors, most of us know the concept of voltage U and current I, where U/I=R is the conductors resistance. 
But in RF/HF, there are situations (e.g. a waveguide) where one cannot simply define U or I anymore, but instead we have to deal with waves. S-parameters just put the wave amplitudes into relation. Take for example a laser pointing into a mirror. The relation of incident and reflected laser beam (waves) is the reflection coefficient or S11. S-Parameters are dimensionless complex numbers.
The Smith Chart is mainly a (very powerful) drawing aid to put these complex numbers onto paper.