What is an inference?

A prediction of test results before an experiment
A retest of experimental results to make them reliable
Background research completed with questioning
A conclusion derived from evidence and logical reasoning

An inference is a conclusion derived from evidence and logical reasoning.

Explanation:

Usually, inferences are made after observing experiments or after observing natural phenomenon at work. The data collected from these observations is later analyzed.  The outcome of this analysis is what draws inferences or conclusions that are used to coin facts or theories.

An example is that it is through analysis of data from seismographs around the world that the inference was made that S-waves of earthquakes cannot pass through the liquid outer core of the earth but P-waves can. This later has been used to probe and study the interior of the earth.

a corroding iron, if that's one of your choices