Vertical scaling
Handling more traffic by moving to a bigger, more powerful machine: more processor, more memory, more disk.
What it tells you about a developer
Reaching for vertical scaling first shows cost pragmatism. Knowing that a bigger database machine solves the problem for two more years, without a rewrite, is judgment that comes from having run systems on real budgets. A developer who can explain when each direction wins has thought about scaling as an economic decision, which reads as senior.
Vertical scaling keeps the system on one machine and makes that machine stronger. It is the plainest way to grow, because nothing about the software has to change. It has a ceiling: machines only get so big, and the biggest ones get expensive fast. Teams often scale vertically first, then go horizontal when they hit the ceiling.