"Laptop" and "notebook" are marketing terms that are generally interchangeable. These computers differ from a tablet primarily in that they have a built-in keyboard, clamshell design and traditionally do not have a touch screen.
Companies that market computers may choose to use the term "notebook" for laptops that are among the smallest and lightest of their product line, but this is not an industry standard or a widespread practice. If the term is used in this way, the notebook may be less powerful and have less memory than other laptops from that manufacturer but is also generally lighter, smaller and has improved battery life.
Some traditional distinctive features of a notebook or laptop are a clamshell design that includes both monitor and keyboard in a folding case and the use of a trackpad, in addition to USB ports for input.
Tablets are smaller and lighter than laptops, and the primary means of input is through a touch screen. While laptops with touch screens do exist, it is considered a standard and defining feature of a tablet. Some tablets may have USB ports or physical keyboards that can be attached, but these are not considered standard.
Tablets also tend to be significantly less powerful than laptops when comparing those that are manufactured and brought to market at roughly the same time.