It is mentioned to be after a long road "beyond the Merlock Mountains", and "through the spider-shadows"; other than that it is unknown if Tode refers to an actual marsh in the Westlands, or if it was just an invention by the poet.
tode is the Middle English spelling for a "toad"; it was also a word with evil connotations, as the toad/frog was considered a demonic creature, according to Wiktionary (cf. abovementioned link). Furthermore, Tode is also the German word for "death". Although the two words are unrelated, and J.R.R. Tolkien didn't specifically explain his choice for the name, both explanations are fitting for an ominous swamp.
|Legendary Locations in Arda|
|Mountains:||Astulat · Mountains of the Moon · Merlock Mountains|
|Regions:||Aerie · Belmarie · Fantasie · Last Desert · Sindanórie · Thellamie · Tode|
|Other:||Caves of the Forgotten · Gorbelgod|