235/60R18 is a tire size specification:
235 = tire width in millimeters
60 = aspect ratio (sidewall height is 60% of the width)
R = radial construction
18 = wheel/rim diameter in inches
This size is commonly used on SUVs and crossovers such as the Honda CR-V, Nissan Rogue, and Toyota RAV4 depending on trim.
Approximate dimensions:
Overall diameter: ~29.1 inches
Sidewall height: ~5.6 inches
Circumference: ~91.5 inches
If you want, I can also help with:
Compatible alternative sizes
Best tires in 235/60R18
Winter vs all-season recommendations
Price comparisons
Load/speed rating explanation
Fitment for a specific vehicle