A question of terminology
Few academic terms cause as much confusion as "dissertation" and "thesis." People use them interchangeably, but the distinction matters when you are reading your faculty guidelines or talking to a supervisor.
It changes by region
In much of the UK and the Commonwealth, including Zambia, a dissertation is the major research project for a masters or undergraduate degree, and a thesis is the larger work submitted for a PhD.
In the United States the convention runs the other way. There a thesis is written for a masters degree and a dissertation for a doctorate.
Because of this, the safest move is to read your own institution's regulations rather than assume.
The real differences are scale and originality
Beyond the label, the two documents differ in ambition. A doctoral thesis is much longer and engages with theory in far more depth. A PhD is expected to make an original contribution to knowledge. A masters dissertation shows that you can apply research methods well, but it does not always have to break new theoretical ground. Doctoral work usually ends with an oral defence. Masters work may or may not.
What stays the same
Both follow a recognisable structure: introduction, literature review, methodology, results, discussion, and conclusion. Both need a clear problem, aligned objectives, a defensible method, and careful referencing. The skills you build on a masters dissertation carry straight over to doctoral work.
What this means for you
If you are a masters student in Zambia, you are almost certainly writing a dissertation. If you are doing a PhD, you are writing a thesis. Either way, the word on the cover matters far less than the quality of the argument inside.
Whichever term applies, examiners look for the same things. They want a focused problem, a coherent argument, suitable methods, honest analysis, and clear writing. Get those right and the label is just a formality. If you are unsure which standard applies, check the faculty handbook first, then confirm with your supervisor before you start.