What is the purpose of characters ".*" in command "sudo dmicode -t 17 | grep "Size.*MB"?

The answer to the physical RAM question is:

sudo dmidecode -t 17 | grep "Size.*MB" | awk '{s+=$2} END {print s / 1024 "GB"}'

Above code gives the correct answer of 8GB on this computer with Unbutu 20.04.3

Please explain why?

There are 4 records (4 rows) with this dmidecode command that greps with "MB:

sudo dmidecode -t 17 | grep "Size.*MB"

Size: 2048 MB
Size: 2048 MB
Size: 2048 MB
Size: 2048 MB

There are 5 records (5 rows) this dmidecode command that greps with "Size":

sudo dmidecode -t 17 | grep "Size" 
Size: 2048 MB
Size: 2048 MB
Size: 2048 MB
Size: 2048 MB
Size: 4096 kB

There are 0 records (zero) with:

sudo dmidecode -t 17 | grep "Size**MB"
sudo dmidecode -t 17 | grep "Size*MB" 
sudo dmidecode -t 17 | grep "Size.?MB" 
sudo dmidecode -t 17 | grep "Size. MB" 
sudo dmidecode -t 17 | grep "Size??MB" 
sudo dmidecode -t 17 | grep "Size???MB" 
sudo dmidecode -t 17 | grep "Size????MB"

Can someone explain how we get 4 records with:

sudo dmidecode -t 17 | grep "Size.*MB"

The 4 records correctly shows the 4 memory sticks of 2048 MB per stick.

Then awk addition correctly gives:

8192 MB = 2048+2048+2048+2048

Then awk division by 1024 we have 8GB.

Can someone clarify what the characters .*are doing in above?

The answer's in man grep: REGEX.

As per grep manpage:

The period . matches any single character.
*  The preceding item will be matched zero or more times.

Command grep "Size.*MB" translates to:

Print all lines containing exact pattern "Size" followed by exact pattern "MB", regardless of how many characters are between the patterns.

The command would also display lines:

SizeMB
Size do-be do-be doo MB
easd EdsSizei up@#$Ahfu e8MBGj;eh di uh7987 p*&(8