Sadly I cannot just add a comment to the above mentioned answer. (since I switched this account over and dont have enough karma yet)
That being said, I will try to clarify and help.
Over all, the answer from Henning is mostly correct with regards to the different words. So nothings needs to be added there.
However, seeing your last comment on his answer, I think the confusion doesn't come from word choice directly but rather from the German companies not beeing consitent in their own language and terminology.
So as an example ... when checking the homepage from DIEHL. (because you choose that as well)
We are able to filter for different job offerings under this link:
Now we can clearly see that under "Level" the company distinguishes between "Abschlussarbeit" and "Praktikum".
Meaning you can filter all job offerings by these terms specifically.
But when I actually used a filter, I did not get consistent results.
For example searching for simple internships ("Praktikum"), I see some results stating "Abschlussarbeit" in the title of the job descriptions as well. If the company would be consistent, then these offerings should be filtered under the option "Abschlussarbeit" accordingly. Yet they are found in the (wrong) section (filtered under "Praktikum").
I put "wrong" in brackets here at the end, because finding these job offerings in other sections could also mean that you don't have to necessary write your Bachelors/Marsters Thesis in these offerings (even though they literally state "Abschlussarbeit") and that you are free to rather apply as a normal internship as well.
It could just mean that the deparment of the company does not care whether you write your thesis or if you just search a normal internship, but they only wanted to put one job desciption and didn't bother with rewriting the title.
What I tried to clarify with this example was -> even as a native german speaker, it is not clear what exactly they search for some of their job offerings.
So lets now come back to your question about "Bachelorand".
A "Bachelorand" is simply just referring to a student who is currently enrolled in a Bachelors program.
Henning is also right since the term is not widely used and is often rather used to refer to someone who is currently writing his Bachelors Thesis. So you usually would not refer to a first year student as "Bachelorand" even though it would be technically correct.
Thus, the word "Bachelorand" in a job description gives you no hint on whether a job offering is just a normal internship ("Praktikum") or a thesis topic ("Abschlussarbeit").
Again using the homepage filter function from DIEHL, we can find job offerings with titles such as "Bachelorand" under both filters "Praktikum" and "Abschlussarbeit".
I assume they generally just refer to "currently enrolled university sudents" with this term.
Depending on the filter that you used, I would then place the offering there. If you found the "Bachelorand" offerings in the "Praktikum" section, I guess they are referring to normal internships and if it was listed under the "Abschlussarbeit" section it should be a thesis topic.
HOWEVER, since we already saw that DIEHL is not consitent here (listing Abschlussarbeit offerings under the Praktikum section, even though they distinguish between these two), I would recommend you to just ask them when in doubt. Like every of their offerings has a telephone number for exactly such reasons.
So even if you find a topic under the "Abschlussarbeit" filter, but you dont want to write a thesis. Just call and ask if it is really required or if they are okay with you just doing a normal internship. They will honestly often not mind this, since they just want students as cheap intermideate workers for their projects. ;)
If you are not comfortable asking them by phone, then you are always free to just apply for the position and state in your application that you specifically want a normal internship and that you are not searching for a thesis topic. If you are unlucky though and they actually wanted a person for a thesis only, then you wasted some effort here, so I would always just ask them first...
NOTE: Having all this said about the terms "Bachelorand", "Praktikum" and "Abschlussarbeit".
If you need an internship, which is part of your final examination mark in your study program, what you are looking for is a "Pflichtpraktikum" as Henning stated correctly. This is important because the company needs to be specific certified to advertise such internships and they need to be accepted by your university as well, so you cannot make them wherever.
If you search on the DIEHL page for "Praktikum" though, you can find job offerings exactly descriped as "Pflichtpraktum" showing on the first page.