You're undoubtedly thinking of Ladino, sometimes known as Judeo-Spanish (djudeoespanyol), Sephardic, Crypto-Jewish, Spanyol and sometimes other names.
Ladino had its origins in 1492, when Jews were expelled from Spain. Over the centuries, the Spanish of the late 15th century as spoken by those Jews was influenced by various Mediterranean languages spoken where the Jews went to live. Today, somewhere between 100,000 and 200,000 people speak Ladino, most of them in Israel, although very few of the people who use it are monolingual. Some advocates of the language fear that it could die out as the speakers more often use the languages of the cultures around them. Although there is one small Ladino newspaper in Turkey, there is little new literature being produced in the language. Only one high school in Jerusalem today has a Ladino language program.
Traditionally, Ladino was written using the Hebrew alphabet with the writing from right to left. Today, the Latin alphabet (the same one used by English and Spanish) is used most commonly except in some religious writings.
Although Ladino is indeed a language in its own right, it and Spanish aren't so different that speakers of the two can't communicate with each other. There are strong and obvious similarities, just as there are, for example, between Spanish and Portuguese.
Here's an example of a portion of a newsgroup posting in Ladino, one I chose because much of it is fairly easy to understand (reading it out loud may make it more comprehensible):
- En komparasion kon las duras sufriensas ke pasaron los reskapados de los kampos de eksterminasion nazistas en Gresia, se puede dizir ke las sufriensas de los olim en el kampo de Kipros no fueron muy grandes, ma despues de anyos de vida en los kampos de konsentrasion, en teribles kondisiones, eyos kerian empesar en una mueva vida en Erets Israel i sus planos eran atrazados agora por unos kuantos mezes.
One notable grammatical difference between Spanish and Ladino is that the latter doesn't use the usted and ustedes forms of the second-person pronoun; their use developed in Spanish after the Jews had left. Similarly, Ladino distinguishes the sounds of the B and the V. Again, it wasn't until after the 15th century that Spaniards gave those two consonants the identical sound. Some other features of Spanish, such as the inverted question mark and the use of the Ñ, are also absent.