For some reason you have hidden virtually all of the useful information from your question. However, yes it would mostly be hackers/bots searching for vulnerabilities. Some entries will be legitimate, and likely related to TCP sessions where your machine thinks the connection has been closed and forgotten, but the remote machine thinks it isn't.
Those log entries are probably from iptables log rules. If you are using UFW, know that it is just a front end for iptables. Notice that 7 out of 16 of your example list are from 188.8.131.52. Please know that particular sub-net is one of a great many that are very bad. This from my iptables rule set, where I DROP the entire sub-net:
doug@s15:~$ sudo iptables -xvnL
Chain INPUT (policy DROP 14 packets, 1478 bytes)
pkts bytes target prot opt in out source destination
2584 103392 DROP all -- enp1s0 * 184.108.40.206/18 0.0.0.0/0
Observe the rule has been hit 2584 times.
EDIT: By the way, I use the following method to find the worst players from the previous day (not including the ones I already specifically DROP):
doug@s15:~$ tail -20000 /var/log/syslog.1 | sed 's/ /\n/g' | grep "SRC=" | cut -d"." -f1,2,3,4 | sort | uniq -c | sort -g | tail -4
doug@s15:~$ tail -20000 /var/log/syslog.1 | sed 's/ /\n/g' | grep "SRC=" | cut -d"." -f1,2,3 | sort | uniq -c | sort -g | tail -4
doug@s15:~$ tail -20000 /var/log/syslog.1 | sed 's/ /\n/g' | grep "SRC=" | cut -d"." -f1,2 | sort | uniq -c | sort -g | tail -4
Note: I use
tail because I often only search the last few hundred lines.
Please, for your next question, give us more information to work with.