This is the type of standardized lingua franca written Arabic you see in Middle Eastern newspapers or the spoken Arabic you might hear on Al Jazeera broadcasts. It does not include dialects or highly colloquial vocabulary or word forms.
A "single Arabic word expression" consists of a word stem, its prefixed and/or suffixed inflections, and possibly a combination of prefixed particles like the definite article "al-" or the monoliteral particles like "wa" (and) or "ka" (as). For example, in Arabic, "and like my sons" would be expressed with a one word cluster having no spaces.
This refers to forms of a word in one of its possibly grammatically contextual shapes including and other than the dictionary citation form, for example, the plural of a noun or the perfect passive of a verb. You do not have to enter a word as it is listed in the dictionary; you can enter this or any contextual form as found in running text.
In normal Arabic as seen in newspapers, the short vowel marks for a, i, and u, and diacritical marks such as sukuun and shadda are not written. These so-called 'points' are used only in pedagogical materials aimed at learners of the language. You can enter these marks in your input expression in order to limit the output, but they are optional.
The citation, canonical, or headword form of a word as it appears in a dictionary. For example, the standard lemma of the Arabic 1st person imperfect verb form "yaktub" is the 3d person singular perfect form of the verb, i.e. "kataba", because this is the form of the verb as normally listed as a headword in Arabic dictionaries.
The English translation or equivalent of an Arabic expression.