Crucial has this as a laptop, using SODIMM (DDR, PC2700) using module sizes up to 1GB - can use unmatched sizes.
SO is "Small outline" - the modules for laptops are smaller (and more expensive) than their desktop counterparts. Not just smaller in size, but the connector is also smaller.
If I remember correctly, DIMM is "dual inline memory module", with at least 4 incompatible variants:
1. SDRAM DIMM (PC66/100/133) - the first example of "full width" memory for the Pentium series.
2. DDR DIMM (PC1600/2100/2700/3200) - Double data rate RAM - faster memory for new chipsets and CPUs
3. DDR2 DIMM - another change
4. SODIMM - small outline versions, probably SO versions of all of them - if not now, then soon.
All of these are 64 bit wide, making them the full with of a 64 bit memory bus.
They were predated by the SIMM - Single Inline memory module, which had 32 bit (full width of a 486, needed two for a full Pentium memory bank) or 8/9 bit (used in 386/486 systems only).
Before that, it was rows of 8 or 16 chips, individually socketed!