What is Knowledge?

Legal Definition
In law knowledge is one of the degrees of mens rea that constitute part of a crime. For example, in English law, the offence of knowingly being a passenger in a vehicle taken without consent (TWOC) requires that the prosecution prove, not only that the defendant was a passenger in a vehicle and that it was taken by the driver without consent, the prosecution must also prove that the defendant knew that it was taken without consent.

Under the principle of ignorantia juris non excusat, ignorance of or mistake about the law is no defence. The mens rea of knowledge refers to knowledge about certain facts. It is "a positive belief that a state of affairs exists."

Knowledge can be actual, constructive, or imputed.
-- Wikipedia
Legal Definition
Information as to a fact. 2. Many acts are perfectly innocent when the party performing them is not aware of certain circumstances attending them for example, a man may pass a counterfeit note and be guiltless, if he did not know it was so he may receive stolen goods if he were not aware of the fact that they were stolen. In these and the like cases it is the guilty knowledge which makes the crime. See, as to the manner of proving guilty knowledge, Archb. Cr. Pl. 110, 111. Vide Animal. Dog; Evidence ignorance; Scienter .
-- Bouviers Law Dictionary
Legal Definition
The difference between "knowledge" and "belief" is nothing more than in the degree of certe inty. With regard to things which make not a very deep impression on the memory, it may be called "belief." "Knowledge" is nothing more than a man's firm belief. The difference is ordinarily merely in the degree, to be judged of by the court, when addressed to the court; by the jury, when addressed to the Jury. Hatch v. Carpenter, 9 Gray (Mass.) 271. See Utley v. Hill, 155 Mo. 232, 55 S. W. 1091, 49 L. R. A. 323, 78 Am. St. Rep. 569; Ohio Valley Coffin Co. v. Goble, 28 Ind. App. 362, 62 N. El 1025; Clarke v. Ingram, 107 Ga. 565, 33 S. E. 802. Knowledge may be classified in a legal sense, as positive and imputed,—imputed, when the means of knowledge exists, known and accessible to the party, and capable of communicating positive information. When there is knowledge, notice, as legally and technically understood, becomes immaterial. It is only material when, in the absence of kn'owledge, it produces the same results. However closely acfual notice may, in many instances, approximate knowledge, and constructive notice may be its equivalent in effect, there may be actual notice without knowledge; and, when constructive notice is made the test to determine priorities of right, it may fall far short of knowledge, and be sufficient. Cleveland Woolen Mills v. Sibert, 81 Ala. 140, 1 South. 773. -
See also
-- Black's Law Dictionary
Legal Definition
Information; acquaintance; notice actual or imputed. See 81 Ala. 140, 1 South. 773. Knuckles. See Brass knuckles. Kyn. Same as Kin.
-- Ballentine's Law Dictionary