buck or booster converter, difference between R RL load
Whether you talk about a boost or a buck converter, it can be loaded by various types of load but let's assume a resistance \$R\$. In the literature, you often find \$L\$, \$C\$ and \$R\$ for the constitutive elements:



Then, if you consider energy-storing elements parasitics like their equivalent series resistance or ESR, writers use lowercase to designate these: \$r_C\$ and \$r_L\$ respectively for the capacitor and the inductor. The sketch for a boost converter thus updates to:



The load resistance can be labeled whatever you want but \$R\$, \$R_L\$ or \$R_{load}\$ will do just fine as long as you respect lower and uppercase notations for consistency.