Primary source - A source created by an eyewitness.
Secondary source - An account based on other sources.
Validity - Assessment of whether a historical source is real.
Reliability - Assessment of whether a historical source's account can be trusted. i.e. Is the source lying?
Bias - The result of allowing personal outlook and preconceptions to color one's interpretation of the facts. Bias may be conscious or unconscious.
Interpretation - A well-considered analysis of the meaning of a historical topic that encompasses all the available evidence in an attempt to reach the truth. Requires research and analysis.
Hypothesis - A tentative assumption made in order to draw out and test its logical or empirical consequences.