Lexeme: Like a word. 無 is a lexeme. 今日 is a lexeme. とした might be three lexemes. 作る is a single lexeme. 作るのだ might be two or three lexemes, depending on whether you consider のだ to be one lexeme or two.
Lemma: The "dictionary" version of a given lexeme. In とした, the lemmas are と する た. In 作りましょう, the lemmas are 作る and ます. Depending on who you ask, ~ou might be a lemma there as well, but the Japanese writing system hides it. 限り and 限る belong to the same lemma, 限る.
Ruby text: When small text is placed next to larger text as a gloss, regardless of the purpose or language of the large or small text. Normal ruby text is furigana/yomigana, but not all ruby text is furigana/yomigana. The term "ruby" comes from a font/size used for glossing in British printing presses or something. In Aozora formatting, ruby text is placed inside 《》, with the associated normal text coming before it, with a | marking its start if it would be ambiguous otherwise. In vnscripts formatting, the associated text is either not marked or is placed in 〈〉. Likewise, it should come before the ruby text.
Segmentation/word splitting: Taking spaceless Japanese text and identifying word boundaries. This is almost always done with some kind of text analysis tool, usually one like like mecab or kuromoji, which work with viterbi graphs to break down hidden markov models. Tools like this give very low error rates on the texts they're trained on, but are not perfect, especially when heavy phonetic slang, kana "misuse", and ad-hoc spellings enter the text. VNs do these things a lot more than the "normal" texts that these tools are generally used on.
Line wrap: When the text goes to a new line in the middle of a paragraph. In VNs, line wraps are generally when the text goes to a new line without waiting for input. However, some games can wait for input even if there's no line wrap at that point in the text at all.
Line break: When the text goes to a new line between sentences.
Page feed: When the text goes to a new page, even if each page is only one line long. In most ADV style games, the overwhelming majority of line breaks are also page feeds.