Which of the following defines an integer?

The correct definition of an integer is whole numbers with no fractional parts. Integers include both positive and negative whole numbers, as well as zero. This means they can be represented as -3, -2, -1, 0, 1, 2, 3, and so on. The absence of decimal or fractional components is what distinctly characterizes integers, making them a fundamental concept in mathematics.

In contrast, the other options describe different concepts. The first option refers to real numbers, which can indeed have decimal parts. The third option describes characters or symbols, which relate to text, not numerical values. The fourth option refers to a collection of characters, which could be a string or sentence, but does not pertain to numeric definitions at all. Thus, option B accurately captures the essence of what integers are within the context of number classification.