Dictionary:

nota bene

  (nō'tə bĕn'ē, bē'nē)

Used to direct attention to something particularly important.

[Latin notā bene, note well : notā, sing. imperative of notāre, to note + bene, well.]

A Windows word processor with enhanced features for writers from Nota Bene Associates, Inc., New York www.notabene.com). The Scholar's Workstation package includes the Nota Bene word processor, Ibidem bibliographic manager and Orbis text retrieval system. Lingua Workstation is Scholar's Workstation plus an advanced multi-lingual module that adds support for Greek, Hebrew, Cyrillic, the International Phonetic Alphabet (IPA) and additional characters in the Roman alphabet. Based on the XyWrite word processing engine, Nota Bene was originally developed in 1983 for DOS by Dragonfly Software.

Lat: note well; written as the original note n.b. to indicate an important portion of the text to be studied.

Mark well.

The noun has one meaning:

Meaning #1: a Latin phrase (or its abbreviation) used to indicate that special attention should be paid to something
  Synonyms: NB, N.B.