A crossword is a word puzzle that usually takes the form of a square or a rectangular grid of white-and black-shaded squares. The game's goal is to fill the white squares with letters, forming words or phrases, by solving clues, which lead to the answers. In languages that are written left-to-right, the answer words and phrases are placed in the grid from left to right and from top to bottom. The shaded squares are used to separate the words or phrases.  

Substantial variants from the usual forms exist. Two of the common ones are barred crosswords, which use bold lines between squares (instead of shaded squares) to separate answers, and circular designs, with answers entered either radially or in concentric circles. "Free form" crosswords ("criss-cross" puzzles), which have simple, asymmetric designs, are often seen on school worksheets, children's menus, and other entertainment for children. Grids forming shapes other than squares are also occasionally used.  

There are several types of wordplay used in cryptics. One is straightforward definition substitution using parts of a word. For example, in one puzzle by Mel Taub, the answer IMPORTANT is given the clue "To bring worker into the country may prove significant". The explanation is that to import means "to bring into the country", the "worker" is a worker ant, and "significant" means important. Here, "significant" is the straight definition (appearing here at the end of the clue), "to bring worker into the country" is the wordplay definition, and "may prove" serves to link the two. Note that in a cryptic clue, there is almost always only one answer that fits both the definition and the wordplay, so that when one sees the answer, one knows that it is the right answerЧalthough it can sometimes be a challenge to figure out why it is the right answer. A good cryptic clue should provide a fair and exact definition of the answer, while at the same time being deliberately misleading. 

Some crossword designers have started including a metapuzzle, or "meta" for short: a second puzzle within the completed puzzle. After the player has correctly solved the crossword puzzle in the usual fashion, the solution forms the basis of a second puzzle. The designer usually includes a hint to the metapuzzle. For instance, the puzzle Eight Isn't Enough by Matt Gaffney gives the clue "This week's contest answer is a three-word phrase whose second word is 'or'." The crossword solution includes the entries "BROUGHT TO NAUGHT", "MIGHT MAKES RIGHT", "CAUGHT A STRAIGHT", and "HEIGHT AND WEIGHT", which are all three-word phrases with two words ending in -ght. The solution to the meta is a similar phrase in which the middle word is "or": "FIGHT OR FLIGHT".  

Every issue of GAMES Magazine contains a large crossword with a double clue list, under the title The World's Most Ornery Crossword; both lists are straight and arrive at the same solution, but one list is significantly more challenging than the other. The solver is prompted to fold a page in half, showing the grid and the hard clues; the easy clues are tucked inside the fold, to be referenced if the solver gets stuck. 

In a diagramless crossword, often called a diagramless for short or, in the UK, a skeleton crossword or carte blanche, the grid offers overall dimensions, but the locations of most of the clue numbers and shaded squares are unspecified. A solver must deduce not only the answers to individual clues, but how to fit together partially built-up clumps of answers into larger clumps with properly set shaded squares. Some of these puzzles follow the traditional symmetry rule, others have left-right mirror symmetry, and others have greater levels of symmetry or outlines suggesting other shapes. If the symmetry of the grid is given, the solver can use it to his/her advantage.  

An acrostic is a type of word puzzle, in eponymous acrostic form, that typically consists of two parts. The first is a set of lettered clues, each of which has numbered blanks representing the letters of the answer. The second part is a long series of numbered blanks and spaces, representing a quotation or other text, into which the answers for the clues fit. In most forms of the puzzle, the first letters of each correct clue answer, read in order from clue A on down the list, will spell out the author of the quote and the title of the work it is taken from; this can be used as an additional solving aid.