A tablet (also known as a pill) is a pharmaceutical oral dosage form (oral solid dosage, or OSD) or solid unit dosage form. Tablets may be defined as the solid unit dosage form of medication with suitable excipients. It comprises a mixture of active substances and excipients, usually in powder form, that are pressed or compacted into a solid dose. The main advantages of tablets are that they ensure a consistent dose of medicine that is easy to consume.

Tablets are prepared either by moulding or by compression. The excipients can include diluents, binders or granulating agents, glidants (flow aids) and lubricants to ensure efficient tabletting; disintegrants to promote tablet break-up in the digestive tract; sweeteners or flavours to enhance taste; and pigments to make the tablets visually attractive or aid in visual identification of an unknown tablet. A polymer coating is often applied to make the tablet smoother and easier to swallow, to control the release rate of the active ingredient, to make it more resistant to the environment (extending its shelf life), or to enhance the tablet's appearance.

Medicinal tablets were originally made in the shape of a disk of whatever colour their components determined, but are now made in many shapes and colours to help distinguish different medicines. Tablets are often imprinted with symbols, letters, and numbers, which allow them to be identified, or a groove to allow splitting by hand. Sizes of tablets to be swallowed range from a few millimetres to about a centimetre.

The compressed tablet is the most commonly seen dosage form in use today. About two-thirds of all prescriptions are dispensed as solid dosage forms, and half of these are compressed tablets. A tablet can be formulated to deliver an accurate dosage to a specific site in the body; it is usually taken orally, but can be administered sublingually, buccally, rectally or intravaginally. The tablet is just one of the many forms that an oral drug can take such as syrups, elixirs, suspensions, and emulsions.

Pills are thought to date back to around 1500 BC. Earlier medical recipes, such as those from 4000 BC, were for liquid preparations rather than solids. The first references to pills were found on papyruses in ancient Egypt and contained bread dough, honey, or grease. Medicinal ingredients, such as plant powders or spices, were mixed in and formed by hand to make little balls, or pills. In ancient Greece, such medicines were known as katapotia ("something to be swallowed"), and the Roman scholar Pliny, who lived from 23 to 79 AD, first gave a name to what we now call pills, calling them pilula.

Pills have always been difficult to swallow, and efforts have been made to make them go down easier. In medieval times, people coated pills with slippery plant substances. Another approach, used as recently as the 19th century, was to gild them in gold and silver, although this often meant that they would pass through the digestive tract with no effect. In the 1800s, sugar coating and gelatin coating were invented, as were gelatin capsules.

In 1843, the British painter and inventor William Brockedon was granted a patent for a machine capable of "Shaping Pills, Lozenges, and Black Lead by Pressure in Dies". The device was capable of compressing powder into a tablet without the use of an adhesive.

A pill was originally defined as a small, round, solid pharmaceutical oral dosage form of medication. The word's etymology reflects the historical concepts of grinding the ingredients with a mortar and pestle and rolling the resultant paste or dough into lumps to be dried. Today, in its strict sense, the word pill still refers specifically to tablets (including caplets) rather than capsules (which were invented much later), but because a simple hypernym is needed to intuitively cover all such oral dosage forms, the broad sense of the word pill is also widely used and includes both tablets and capsules — colloquially, any solid oral form of medication falls into the "pill" category (see pill § Usage notes).