A translation memory system does not create a machine translation; rather, it is a method of re-using previous translations.

The translation memory, a database of translations, contains sections of text in the source language stored together with the corresponding text in the target language as "segment pairs".

The text sections are first divided into segments according to previously defined rules. Markers used as segment ends are for example full stops (end of sentence) or paragraph markers. Segments are therefore usually sentences, lists or table elements.

Any new text is compared with the segments previously stored in the database. The translation memory system determines matching source language segments and offers the saved, equivalent segment in the target language as an existing translation. Similar segments are also recognised and offered as so-called fuzzy matches.

When a new document has been analysed against an existing translation memory, the resulting segments are divided into four categories:

Perfect Matches (100 % match):

A segment in the new document is identical to a segment stored in the translation memory.

Repetitions:

The same segment exists several times in the current document. This segment only has to be translated once. When the segment is repeated, the translation is automatically supplied by the translation memory.

Fuzzy Matches (75-99 % match):

A segment in the source text is partially identical to a segment in the translation database.

No Matches (0-74 % match):

No similar segment has been found. The text must be newly translated.

During the translation process, the translation memory system marks the analysed segments in the target text and labels them with the match percentage. The translator can choose to accept the suggested translation, adapt it or discard it altogether and enter a new translation. Each new translation is in turn stored in the translation memory and is therefore available for use in future projects.

Source:

http://www.dicits.com/en/faq/wie-funktionieren-tm-systeme.html.