Several terms in constant use among readers describe handling rather than cards, and their histories are not alike.
A reversed card is one that arrives upside down relative to the reader, and most modern readers give it a different sense from the same card upright, commonly a blocked, internalised, delayed or excessive form of the upright meaning, sometimes a flat negation of it. Practice here is genuinely divided and always has been. Some readers use reversals throughout, some never do and deliberately square the deck so that none can appear, and some read them only in particular positions of a spread. Nothing in the tarot's history requires them. The deck began as a card game in fifteenth-century Italy, where orientation carried no significance at all, and reversed meanings appear in the divinatory literature only from the late eighteenth century, with Etteilla among the first to publish them systematically. A reader who declines to use reversals is not neglecting a tradition. They are choosing one of two established conventions, and the choice should be stated at the start of a reading rather than left for the querent to work out.
A significator is a card chosen before the reading to stand for the querent or for the matter in hand, and laid down as the base that the rest of the spread refers back to. It is usually a court card selected by the querent's colouring, age and temperament, or by their astrological sign; some readers instead pick a Major Arcana card matched to the question. The practice reaches modern readers through the Golden Dawn material and Waite's instructions for the Celtic Cross. It has largely fallen out of use, and one reason is plain enough: choosing a person-card by physical appearance is a nineteenth-century convention that reads very poorly now.
A clarifier is an additional card drawn when a position is unclear, laid beside the card it is meant to explain rather than replacing it. It is modern, informal, and readers warn each other about it, because the temptation to keep drawing until the answer improves is obvious and the discipline of sitting with an unwelcome card is generally held to be the point of the exercise.
A shadow card is the card left at the bottom of the deck after cutting, in some methods the one lying beneath the significator, read as the influence underneath the question that the querent has not put into words. The name borrows from Jungian vocabulary, and the practice is recent: late twentieth century at the earliest, and spread mainly through the online reading community rather than through any published system.