What is the difference between crystals and solid? In condensed matter physics, what are the differences between crystals.
 A: Solids are rigid and resist a change in volume. There are three general types of solid:

As you can see from the picture, a crystal is a solid for which the atoms/molecules are highly ordered to form a periodic lattice.
Examples of (poly)crystalline solids include diamond and table salt.
Examples of non-crystalline solids include glass and amorphous calcium carbonate.
A: Technically speaking all solids have crystalline structure. Anything that is truly amorphous is known as supercooled liquid  (such as glass). Depending on how well crystals are oriented they can be divided into two categories, as pointed out by @lemon, single crystals and polycrystals. Single crystals have nearly perfect orientation of sizes few mm long. Polycrystals have sizes few microns. There is another category of crystals that is nanoparticles having sizes ~100 nm. 
I would like to add that most forms of carbon have crystalline structure. Graphite has crystalline structure, diamond has crystalline structure. Most wooden charcole has grahphine like crystalline structure.  Soot is most amorphous and in my opinion it is not truly solid. Paper has crystalline structure, paper is made of tissues which is made from protiens and protiens have crystalline structure. Carbohydrates have crystalline structure, fat is liquid. Ice has crystalline structure. 
If you think about anything 'Hmm... it don't look crystalline' think again there is a fair chance that the thing has crystalline structure. 
