What is a final undergraduate paper called in English?

In my experience, in Mathematics, in the U.S., (where "senior year" is typically the last year of an undergraduate degree), things done beyond literal coursework can be called "senior project", "senior thesis", "honors thesis", "senior writing project", or nearly anything similar, with no precise sense from university to university or even from student to student. That is, sometimes "honors thesis" has some actual requirement beyond "senior thesis", but not reliably so...

The term undergraduate dissertation, or Final Year Project Dissertation is also used. The word Thesis is usually reserved for a PHd or research degree.

As already mentioned this is very dependent on local terminology and will vary from country to country, discipline to disciple and institution to institution.

Thanks to the Bologna Declaration, the degree system is standardized between European countries, among which Croatia. In this system, the 'undergraduate' degree is called a Bachelor degree. Anyone familiar with European education will not confuse this term with any other degrees, and is likely reminded that you are talking about European education, which may have different requirements for various degrees depending on each country.

As such, the following terms will describe what you mean, without confusing your peers (other than those simply unaware of differences between educational systems). Pick the one that closest resembles what your project actually encompasses - for example, mine was called the Bachelor Final Project because it did not require an extensive report.

• Bachelor thesis
• Bachelor end/final project/paper
• Bachelor dissertation

Note that native BrE or AmE speakers may not agree, but I would like to stress that this may be a cultural difference, not a lingual difference: above phraseology might be quite uncommon because the concept of a bachelor thesis is unfamiliar to academics in the UK or US; I have however seen numerous terms like the above at various continental European universities.