Background to the below-mentioned categories of Muktzah:

A. The Rabbis forbid using an object that is expected to remain unused throughout Shabbat, as using it is considered a form of Melacha of having "created" that object for Shabbat use. (Muktzah literally means that the object was set aside in one's mind, not to be used on Shabbat.)

B. During the time of Nechemia, the Rabbis prohibited the movement of some items as a reaction to people who engaged in business activities on Shabbat (see Nechemia 13:15). It was prohibited for the following reasons:

1. as a protective "fence" for Hotza'ah

2. in order to prevent doing a Melacha [accidentally] on Shabbat -- e.g. with a hammer or a pen

3. to maintain the awareness of the uniqueness of Shabbat

CATEGORIES OF MUKTZAH:

Category A. Muktzah objects that may not be used or moved on Shabbat.

1. Muktzah Machmat Chisaron Kis (lit. "Muktzah because of monetary loss"):

These are objects that are either never used, or are used for Melacha exclusively and would not be used for something else on Shabbat (e.g. as a paperweight), out of fear they would be ruined or lost. Examples: expensive items (e.g. camera, decorative vase), professional tools (e.g. a surgical knife), merchandise to be sold, expensive or important documents.

As a general rule, items in this category are defined as being kept in a specific [safe] place, as opposed to "just left lying around."

2. Dachiya b'Yadayim v'Lo Chazi (lit. "pushed aside with the hands and not usable"):

These are objects which one didn't expect to use on Shabbat, because they were placed before Shabbat in a situation where they are: a) not usable (probably until after Shabbat), and b) not in your control to make them usable (during Shabbat).

For example, if one is drying grapes in the sun in order to turn them into raisins (generally a process of a few days), since they first ferment and are inedible, and to become edible depends on the intensity of the sun, they are Muktzah even if the grapes unexpectedly ferment into raisins on Shabbat.

So, too, if one hangs wet laundry outside before Shabbat, during a time of year when one does not expect it to dry during Shabbat, even if the laundry does dry on Shabbat, it is Muktzah and may not be either used or moved. (Laundry that is merely damp at the outset of Shabbat, may be moved once it becomes dry.)

In cases where the outcome is under human control and the object becomes usable on Shabbat, it is not Muktzah and may be used and moved on Shabbat. For example, one may remove edible [frozen] food from the freezer to eat on Shabbat.

3. Muktzah Machmat Issur (lit. "Muktzah because of a prohibition"):

These are objects whose use was prohibited from the beginning of Shabbat because of some other prohibition -- e.g. a fruit hanging on a tree, silverware that lacks tevillah, untithed produce, chametz on Pesach, clothing containing Shatnez.

Included in this category is Muktzah Machmat Mitzvah ("Muktzah due to a prior mitzvah designation) -- e.g. decorations on the walls of a Sukkah, Chanukah oil. In all cases (e.g. even if the fruit fell to the ground) it is still prohibited to use or move the object.