This fallacy get its name from the Latin phrase "post hoc, ergo propter hoc," which translates as "after this, therefore because of this."
Assuming that because B comes after A, A caused B.
Of course, sometimes one event really does cause another one that comes later...
For example, if I register
For a class, and my name later appears on the roll, it's true that the first event caused the one that comes later. But sometimes two events that seem related in time aren't related as cause and event. That is, correlation isn't the same thing as causation.
Example: "President Jones raised taxes, and then the rate of the violent crime went up. Jones is responsible for the rise in crime." The increase in taxes might or might not be one factor in the rising crime rates, but the argument hasn't shown us that one caused the other :-)